774323e378 ci: Force `--enable-external-signer` to prevent future regressions (Hennadii Stepanov)
69978858a4 build: Fix Boost.Process check for Boost 1.73 and older (Hennadii Stepanov)
2199ef79cb build: Fix a non-portable use of `test` (Hennadii Stepanov)
d436c488d4 build, refactor: Replace tabs with spaces (Hennadii Stepanov)
Pull request description:
On master (5f44c5c428) Boost.Process check false fails without the `-lpthread` flag.
```
$ grep -C 2 pthread_detach config.log
/usr/bin/ld: /tmp/cczCQfQv.o: in function `boost::asio::detail::posix_global_impl<boost::asio::system_context>::~posix_global_impl()':
conftest.cpp:(.text._ZN5boost4asio6detail17posix_global_implINS0_14system_contextEED2Ev[_ZN5boost4asio6detail17posix_global_implINS0_14system_contextEED5Ev]+0xa3): undefined reference to `pthread_join'
/usr/bin/ld: conftest.cpp:(.text._ZN5boost4asio6detail17posix_global_implINS0_14system_contextEED2Ev[_ZN5boost4asio6detail17posix_global_implINS0_14system_contextEED5Ev]+0xc4): undefined reference to `pthread_detach'
collect2: error: ld returned 1 exit status
configure:26674: $? = 1
```
Not required for Boost 1.74+.
ACKs for top commit:
laanwj:
Code review ACK 774323e378, is a bugfix/workaround, seems fine to merge last minute for 23.0.
Tree-SHA512: 2a9d4b67fd8910e107af972d8c223286b7c933bc310616f86c8b6d8c903438916980fc76bd7e37f2698f6ce5361dc706cbf2933d1ac2c081bcabe1b83ca7d6b6
25290071c4