315a4d3 build: fix ASLR for bitcoin-cli on Windows (fanquake)

Pull request description:

  ASLR is not currently working for the `bitcoin-cli.exe` binary. This is
  due to it not having a .reloc section, which is stripped by default by
  the mingw-w64 ld we use for gitian builds. A good summary of issues with
  ld and mingw-w64 is available in this thread:
  https://sourceware.org/bugzilla/show_bug.cgi?id=19011.

  All other Windows binaries that we distribute (bitcoind, bitcoin-qt,
  bitcoin-wallet, bitcoin-tx and test_bitcoin) do not suffer this issue,
  and currently having working ASLR. This is due to them exporting
  (inadvertent or not) libsecp256k1 symbols, and, as a result, the .reloc
  section is not stripped by ld.

  This change is a temporary workaround, also the same one described here:
  https://www.kb.cert.org/vuls/id/307144/, that causes main() to be
  exported. Exporting a symbol will mean that the .reloc section is not
  stripped, and ASLR will function correctly.

  Ultimately, this will be fixed by using a newer version of binutils (that has this [change](https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=dc9bd8c92af67947db44b3cb428c050259b15cd0)). Whether that's through bumping our gitian distro, or Guix.

  Related to bitcoin#18629, which has a bunch of additional information in the PR description. If you would like to verify whether or not ASLR is indeed working, with or without this change. One easy way to check is using a tool like [VMMap](https://docs.microsoft.com/en-us/sysinternals/downloads/vmmap).

  Here are the memory mappings for the 0.20.0rc1 `bitcoind.exe` and `bitcoin-cli.exe` binaries. You'll notice that over machine restarts, even though the image is marked `(ASLR)` (which I assume may be due to the header bit being set), no ASLR is actually occuring for `bitcoin-cli.exe`:

  #### bitcoind.exe

  ![bitcoind-1](https://user-images.githubusercontent.com/863730/79678203-74065c80-822b-11ea-90bc-9c883d0aeefa.png)

  ![bitcoind-2](https://user-images.githubusercontent.com/863730/79678204-7668b680-822b-11ea-9263-3e7ba22f904c.png)

  ![bitcoind-3](https://user-images.githubusercontent.com/863730/79678206-7963a700-822b-11ea-972f-af31a514b9b4.png)

  #### bitcoin-cli.exe

  ![bitcoin-cli-1](https://user-images.githubusercontent.com/863730/79678208-7ec0f180-822b-11ea-8480-a4b5d1762945.png)

  ![bitcoin-cli-2](https://user-images.githubusercontent.com/863730/79678213-81bbe200-822b-11ea-964d-994f58ff12b0.png)

  ![bitcoin-cli-3](https://user-images.githubusercontent.com/863730/79678215-84b6d280-822b-11ea-9cd6-fee2e239c003.png)

ACKs for top commit:
  dongcarl:
    ACK 315a4d3
  laanwj:
    ACK 315a4d3

Tree-SHA512: 95f4dc15420ed9bcdeacb763e11c3c7e563eec594a172746fa0346c13f97db3a8769357dffc89fea1e57ae67133f337b1013a73b584662f5b6c4d251ca20a2b1

ASLR is not currently working for the bitcoin-cli.exe binary. This is
due to it not having a .reloc section, which is stripped by default by
the mingw-w64 ld we use for gitian builds. A good summary of issues with
ld and mingw-w64 is available in this thread:
https://sourceware.org/bugzilla/show_bug.cgi?id=19011.

All other Windows binaries that we distribute (bitcoind, bitcoin-qt,
bitcoin-wallet, bitcoin-tx and test_bitcoin) do not suffer this issue,
and currently having working ASLR. This is due to them exporting
(inadvertent or not) libsecp256k1 symbols, and, as a result, the .reloc
section is not stripped by ld.

This change is a temporary workaround, also the same one described here:
https://www.kb.cert.org/vuls/id/307144/, that causes main() to be
exported. Exporting a symbol will mean that the .reloc section is not
stripped, and ASLR will function correctly.

Github-Pull: bitcoin#18702
Rebased-From: 315a4d3

7f7548d rpc: Do not advertise dumptxoutset as a way to flush the chainstate (MarcoFalke)
a9ca65b Fix naming of macOS SDK and clarify version (Andrew Chow)
54d2063 Do not expose and consider -logthreadnames when it does not work (Hennadii Stepanov)
6986b26 build: fix ASLR for bitcoin-cli on Windows (fanquake)
1d1e358 build: Set libevent minimum version to 2.0.21 (Hennadii Stepanov)
842b13a Avoid non-trivial global constants in SHA-NI code (Pieter Wuille)
ade4185 gitian: Add missing automake package to gitian-win-signer.yml (Andrew Chow)

Pull request description:

  Currently backports the following to the 0.20 branch:

  * #18598 - gitian: Add missing automake package to gitian-win-signer.yml
  * #18702 - build: fix ASLR for bitcoin-cli on Windows
  * #18676 - build: Check libevent minimum version in configure script
  * #18665 - Do not expose and consider -logthreadnames when it does not work
  * #18553 - Avoid non-trivial global constants in SHA-NI code
  * #18589 - Fix naming of macOS SDK and clarify version

ACKs for top commit:
  laanwj:
    ACK 7f7548d

Tree-SHA512: 2cba748414a440e3fb901940085a7ae059e8b926c9187fbbbdeb7846a32e7374f318cc21e499c911ff803c42aef2c844b04af10b87f9c5a2b3edf6deb03ebb04

The binutils we use for gitian builds strips the reloc section from
Windows binaries, which breaks ASLR. As a temporary workaround, export
main(). This is the same workaround as bitcoin#18702 (bitcoin-cli), and will
fix the currently failing security check:
```bash
+ make -j1 -C src check-security
make: Entering directory '/home/ubuntu/build/bitcoin/distsrc-x86_64-w64-mingw32/src'
Checking binary security...
bitcoin-util.exe: failed RELOC_SECTION
make: *** [check-security] Error 1
```

Relevant upstream issue:
https://sourceware.org/bugzilla/show_bug.cgi?id=19011

The binutils we use for gitian builds strips the reloc section from
Windows binaries, which breaks ASLR. As a temporary workaround, export
main(). This is the same workaround as bitcoin#18702 (bitcoin-cli), and will
fix the currently failing security check:
```bash
+ make -j1 -C src check-security
make: Entering directory '/home/ubuntu/build/bitcoin/distsrc-x86_64-w64-mingw32/src'
Checking binary security...
bitcoin-util.exe: failed RELOC_SECTION
make: *** [check-security] Error 1
```

Relevant upstream issue:
https://sourceware.org/bugzilla/show_bug.cgi?id=19011

c061800 build: fix RELOC_SECTION security check for bitcoin-util (fanquake)

Pull request description:

  The binutils we use for gitian builds strips the reloc section from
  Windows binaries, which breaks ASLR. As a temporary workaround, export
  main(). This is the same workaround as #18702 (bitcoin-cli), and will
  fix the currently failing security check:
  ```bash
  + make -j1 -C src check-security
  make: Entering directory '/home/ubuntu/build/bitcoin/distsrc-x86_64-w64-mingw32/src'
  Checking binary security...
  bitcoin-util.exe: failed RELOC_SECTION
  make: *** [check-security] Error 1
  ```

  Relevant upstream issue:
  https://sourceware.org/bugzilla/show_bug.cgi?id=19011

ACKs for top commit:
  dongcarl:
    ACK c061800
  laanwj:
    ACK c061800

Tree-SHA512: a1a4da0b2cddfc377190b9044a04f42a859ca79f11ce2c2ab4c3d066a2786c34d5446d75f8eec634f308d2d3349ebbd7c9f76dcaebeeb28e471c829851592367

…oin-util

c061800 build: fix RELOC_SECTION security check for bitcoin-util (fanquake)

Pull request description:

  The binutils we use for gitian builds strips the reloc section from
  Windows binaries, which breaks ASLR. As a temporary workaround, export
  main(). This is the same workaround as bitcoin#18702 (bitcoin-cli), and will
  fix the currently failing security check:
  ```bash
  + make -j1 -C src check-security
  make: Entering directory '/home/ubuntu/build/bitcoin/distsrc-x86_64-w64-mingw32/src'
  Checking binary security...
  bitcoin-util.exe: failed RELOC_SECTION
  make: *** [check-security] Error 1
  ```

  Relevant upstream issue:
  https://sourceware.org/bugzilla/show_bug.cgi?id=19011

ACKs for top commit:
  dongcarl:
    ACK c061800
  laanwj:
    ACK c061800

Tree-SHA512: a1a4da0b2cddfc377190b9044a04f42a859ca79f11ce2c2ab4c3d066a2786c34d5446d75f8eec634f308d2d3349ebbd7c9f76dcaebeeb28e471c829851592367

The binutils we use for gitian builds strips the reloc section from
Windows binaries, which breaks ASLR. As a temporary workaround, export
main(). This is the same workaround as bitcoin#18702 (bitcoin-cli), and will
fix the currently failing security check:
```bash
+ make -j1 -C src check-security
make: Entering directory '/home/ubuntu/build/bitcoin/distsrc-x86_64-w64-mingw32/src'
Checking binary security...
bitcoin-util.exe: failed RELOC_SECTION
make: *** [check-security] Error 1
```

Relevant upstream issue:
https://sourceware.org/bugzilla/show_bug.cgi?id=19011

ASLR is not currently working for the bitcoin-cli.exe binary. This is
due to it not having a .reloc section, which is stripped by default by
the mingw-w64 ld we use for gitian builds. A good summary of issues with
ld and mingw-w64 is available in this thread:
https://sourceware.org/bugzilla/show_bug.cgi?id=19011.

All other Windows binaries that we distribute (bitcoind, bitcoin-qt,
bitcoin-wallet, bitcoin-tx and test_bitcoin) do not suffer this issue,
and currently having working ASLR. This is due to them exporting
(inadvertent or not) libsecp256k1 symbols, and, as a result, the .reloc
section is not stripped by ld.

This change is a temporary workaround, also the same one described here:
https://www.kb.cert.org/vuls/id/307144/, that causes main() to be
exported. Exporting a symbol will mean that the .reloc section is not
stripped, and ASLR will function correctly.

Github-Pull: #18702
Rebased-From: 315a4d3