Backport of core PR15849.

The first commit disables thread_local on some platforms and is not ported:

• The Darwin exclusion is no longer needed since D5514.
• The MinGw exclusion does not seem necessary, at least with our version. The tests run fine on Windows, both 32 and 64 bits.

Also see D2219 which removes the thread_local check.

This introduces a number of bugs:

• This is breaking the build for some *BSD.
• This makes some Unix tools inefficient, like ps or killall.
• Some thread names are truncated and cannot be differentiated.

The fixes will be ported in their own diff for readability.

ninja check
make check

Run the Gitian builds.

Run test_bitcoin.exe on Windows (32 bits) for sanity.
Builld and run the tests on OSX.

Start bitcoind with -logthreadnames=1 and check the debug log
contains the
thread names.