Test on macOS 12.2.1 against the master branch. #24397 doesn't fix it.

```
brew info boost
boost: stable 1.78.0 (bottled), HEAD
...
./configure --enable-external-signer
...
checking for boostlib >= 1.64.0 (106400)... yes
checking whether Boost.Process can be used... no
configure: error: External signing is not supported for this Boost version
```

It does work with boost 1.76 (there was no 1.77 release in home-brew):

```
brew install boost@1.76
...
LDFLAGS="-L/usr/local/opt/boost@1.76/lib" CPPFLAGS="-I/usr/local/opt/boost@1.76/include" ./configure --enable-external-signer
...
checking for boostlib >= 1.64.0 (106400)... yes
checking whether Boost.Process can be used... yes
...
Options used to compile and link:
  external signer = yes
```

There's nothing in the release notes about Boost.Process for either [1.77](https://www.boost.org/users/history/version_1_77_0.html) or [1.78](https://www.boost.org/users/history/version_1_78_0.html).

The Homebrew [formula changes](https://github.com/Homebrew/homebrew-core/commits/master/Formula/boost.rb) are nothing but a trivial version and hash bump.
{
    return std::thread::hardware_concurrency();
}
int64_t GetStartupTime()
{
    return nStartupTime;
}
fs::path AbsPathForConfigVal(const fs::path& path, bool net_specific)
{
    if (path.is_absolute()) {
        return path;
    }
    return fsbridge::AbsPathJoin(net_specific ? gArgs.GetDataDirNet() : gArgs.GetDataDirBase(), path);
}
void ScheduleBatchPriority()
{
#ifdef SCHED_BATCH
    const static sched_param param{};
    const int rc = pthread_setschedparam(pthread_self(), SCHED_BATCH, &param);
    if (rc != 0) {
        LogPrintf("Failed to pthread_setschedparam: %s\n", strerror(rc));
    }
#endif
}
namespace util {
#ifdef WIN32
WinCmdLineArgs::WinCmdLineArgs()