…d hierarchy

e2c40a4 guix-attest: Error out if SHA256SUMS is unexpected (Carl Dong)
4cc35da Rewrite guix-{attest,verify} for new hier (Carl Dong)
28a9c9b Make SHA256SUMS fragment right after build (Carl Dong)

Pull request description:

  Based on:  bitcoin#22075
  Code reviewers: I recommend reading the new `guix-{attest,verify}` files instead of trying to read the diff

  The following changes resolve many usability improvements which were pointed out to me:
  1. Some maintainers like to extract their "uncodesigned tarball" inside the `output/` directory, resulting in the older `guix-attest` mistakenly attesting to the extracted contents
  2. Maintainers whose GPG keys reside on an external smartcard often need to physically interact with the smartcard as a way to approve the signing operation, having one signature per platform means a lot of fidgeting
  3. Maintainers wishing to sign on a separate machine now has the option of transferring only a subtree of `output/`, namely `output/*/SHA256SUMS.part`, in order to perform a signature (you may need to specify an `$OUTDIR_BASE` env var)
  4. An `all.SHA256SUMS` file should be usable as the base `SHA256SUMS` in bitcoin core torrents and on the release server.

  For those who sign on an separate machine than the one you do builds on, the following steps will work:
  1. `env GUIX_SIGS_REPO=/home/achow101/guix.sigs SIGNER=achow101 NO_SIGN=1 ./contrib/guix/guix-attest`
  2. Copy `/home/achow101/guix.sigs/<tag>/achow101` (which does not yet have signatures) to signing machine
  3. Sign the `SHA256SUMS` files:
      ```bash
      for i in "<path-to-achow101>/*.SHA256SUMS"; do
          gpg --detach-sign --local-user "<your-key-here>" --armor --output "$i"{.asc,}
      done
      ```
  5. Upload `<path-to-achow101>` (now with signatures) to `guix.sigs`

  -----

  After this change, output directories will now include a `SHA256SUMS.part` fragment, created immediately after a successful build:
  ```
  output
  └── x86_64-w64-mingw32
      ├── bitcoin-4e069f7589da-win64-debug.zip
      ├── bitcoin-4e069f7589da-win64-setup-unsigned.exe
      ├── bitcoin-4e069f7589da-win64.zip
      ├── bitcoin-4e069f7589da-win-unsigned.tar.gz
      └── SHA256SUMS.part
  ```

  These `SHA256SUMS.part` fragments look something like:
  ```
  3ebd7262b1a0a5bb757fef1f70e7e14033c70f98c059bc4dbfee5d1992b25825  dist-archive/bitcoin-4e069f7589da.tar.gz
  def2e7d3de5ab3e3f955344e75151df4f33713f9101f5295bd13c9375bdf633b  x86_64-w64-mingw32/bitcoin-4e069f7589da-win64-debug.zip
  643049fe3ee4a4e83a1739607e67b11b7c9b1a66208a6f35a9ff634ba795500e  x86_64-w64-mingw32/bitcoin-4e069f7589da-win64-setup-unsigned.exe
  a247a1ccec0ccc2e138c648284bd01f6a761f2d8d6d07d91b5b4a6670ec3f288  x86_64-w64-mingw32/bitcoin-4e069f7589da-win-unsigned.tar.gz
  fab76a836dcc592e39c04fd2396696633fb6eb56e39ecbf6c909bd173ed4280c  x86_64-w64-mingw32/bitcoin-4e069f7589da-win64.zip
  ```

  Meaning that they are valid `SHA256SUMS` files when `sha256sum --check`'d at the `guix-build-*/output` directory level

  When `guix-attest` is invoked, these `SHA256SUMS.part` files are combined and sorted (by `-k2`, `LC_ALL=C`) to create:

  1. `noncodesigned.SHA256SUMS` for a manifest of all non-codesigned outputs, and
  3. `all.SHA256SUMS` for a manifest of all outputs including non-codesigned outputs

  Then both files are signed, resulting in the following `guix.sigs` hierarchy:
  ```
  4e069f7/
  └── dongcarl
      ├── all.SHA256SUMS
      ├── all.SHA256SUMS.asc
      ├── noncodesigned.SHA256SUMS
      └── noncodesigned.SHA256SUMS.asc
  ```

ACKs for top commit:
  achow101:
    ACK e2c40a4
  hebasto:
    ACK e2c40a4, tested on Linux Mint 20.1 (x86_64) with and w/o `NO_SIGN=1`. Changes in `contrib/guix/libexec/codesign.sh` and `contrib/guix/guix-verify` are reviewed only.

Tree-SHA512: 618aacefb0eb6595735a9ab6a98ea6598fce65f9ccf33fa1e7ef93bf140c0f6cfc16e34870c6aa3e4777dd3f004b92a82a994141879870141742df948ec59c1f

9f01fed guix/build: Remove vestigial SKIPATTEST.TAG (Carl Dong)

Pull request description:

  No longer needed or referenced by anything. A relic from prior to the great hierarchy overhaul of #22182

ACKs for top commit:
  achow101:
    ACK 9f01fed
  fanquake:
    ACK 9f01fed

Tree-SHA512: a94cf63f0c5cb8dbacf1025b6c0e81b219c2a3c93b3cbcefc239ccde29e602ecd4b717b1d93dbe53cb791a5017236fb09823c034aec42b0c31894fc9e0ab8b21

9f01fed guix/build: Remove vestigial SKIPATTEST.TAG (Carl Dong)

Pull request description:

  No longer needed or referenced by anything. A relic from prior to the great hierarchy overhaul of bitcoin#22182

ACKs for top commit:
  achow101:
    ACK 9f01fed
  fanquake:
    ACK 9f01fed

Tree-SHA512: a94cf63f0c5cb8dbacf1025b6c0e81b219c2a3c93b3cbcefc239ccde29e602ecd4b717b1d93dbe53cb791a5017236fb09823c034aec42b0c31894fc9e0ab8b21