…xec in RunCommandJSON"

faa1c3e Revert "Merge bitcoin#32343: common: Close non-std fds before exec in RunCommandJSON" (MarcoFalke)

Pull request description:

  After a fork() in a multithreaded program, the child can safely
  call only async-signal-safe functions (see [signal-safety(7)](https://www.man7.org/linux/man-pages/man7/signal-safety.7.html))
  until such time as it calls execv.

  The standard library (`std` namespace) is not async-signal-safe. Also, `throw`, isn't.

  There was an alternative implementation using `readdir` (bitcoin#32529), but that isn't async-signal-safe either, and that implementation was still using `throw`.

  So temporarily revert this feature.

  A follow-up in the future can add it back, using only async-signal-safe functions, or by using a different approach.

  Fixes bitcoin#32524
  Fixes bitcoin#33015
  Fixes bitcoin#32855

  For reference, a failure can manifest in the GCC debug mode:

  * While `fork`ing, a debug mode mutex is held (by any other thread).
  * The `fork`ed child tries to use the stdard libary before `execv` and deadlocks.

  This may look like the following:

  ```
  (gdb) thread apply all bt

  Thread 1 (Thread 0xf58f4b40 (LWP 774911) "b-httpworker.2"):
  #0  0xf7f4f589 in __kernel_vsyscall ()
  #1  0xf79e467e in ?? () from /lib32/libc.so.6
  #2  0xf79eb582 in pthread_mutex_lock () from /lib32/libc.so.6
  #3  0xf7d93bf2 in ?? () from /lib32/libstdc++.so.6
  #4  0xf7d93f36 in __gnu_debug::_Safe_iterator_base::_M_attach(__gnu_debug::_Safe_sequence_base*, bool) () from /lib32/libstdc++.so.6
  #5  0x5668810a in __gnu_debug::_Safe_iterator_base::_Safe_iterator_base (this=0xf58f13ac, __seq=0xf58f13f8, __constant=false) at /bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/debug/safe_base.h:91
  #6  0x56ddfb50 in __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<int*, std::__cxx1998::vector<int, std::allocator<int> > >, std::__debug::vector<int, std::allocator<int> >, std::forward_iterator_tag>::_Safe_iterator (this=0xf58f13a8, __i=3, __seq=0xf58f13f8) at /bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/debug/safe_iterator.h:162
  #7  0x56ddfacb in __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<int*, std::__cxx1998::vector<int, std::allocator<int> > >, std::__debug::vector<int, std::allocator<int> >, std::bidirectional_iterator_tag>::_Safe_iterator (this=0xf58f13a8, __i=3, __seq=0xf58f13f8) at /bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/debug/safe_iterator.h:539
  bitcoin#8  0x56ddfa5b in __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<int*, std::__cxx1998::vector<int, std::allocator<int> > >, std::__debug::vector<int, std::allocator<int> >, std::random_access_iterator_tag>::_Safe_iterator (this=0xf58f13a8, __i=3, __seq=0xf58f13f8) at /bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/debug/safe_iterator.h:687
  bitcoin#9  0x56ddd3f6 in std::__debug::vector<int, std::allocator<int> >::begin (this=0xf58f13f8) at /bin/../lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/debug/vector:300
  bitcoin#10 0x57d83701 in subprocess::detail::Child::execute_child (this=0xf58f156c) at ./util/subprocess.h:1372
  bitcoin#11 0x57d80a7c in subprocess::Popen::execute_process (this=0xf58f1cd8) at ./util/subprocess.h:1231
  bitcoin#12 0x57d6d2b4 in subprocess::Popen::Popen<subprocess::input, subprocess::output, subprocess::error, subprocess::close_fds> (this=0xf58f1cd8, cmd_args="fake.py enumerate", args=..., args=..., args=..., args=...) at ./util/subprocess.h:964
  bitcoin#13 0x57d6b597 in RunCommandParseJSON (str_command="fake.py enumerate", str_std_in="") at ./common/run_command.cpp:27
  bitcoin#14 0x57a90547 in ExternalSigner::Enumerate (command="fake.py", signers=std::__debug::vector of length 0, capacity 0, chain="regtest") at ./external_signer.cpp:28
  bitcoin#15 0x56defdab in enumeratesigners()::$_0::operator()(RPCHelpMan const&, JSONRPCRequest const&) const (this=0xf58f2ba0, self=..., request=...) at ./rpc/external_signer.cpp:51
  ...
  (truncated, only one thread exists)
  ```

ACKs for top commit:
  fanquake:
    ACK faa1c3e
  darosior:
    ACK faa1c3e

Tree-SHA512: 602da5f2eba08d7fe01ba19baf411e287ae27fe2d4b82f41734e05b7b1d938ce94cc0041e86ba677284fa92838e96ebee687023ff28047e2b036fd9a53567e0a