[Development] thread_local: replacing GCC with Clang for MinGW

[Thiago Macieira]

Restarting the thread since it changed subjects many times and has gone back 
and forth.

Simon wrote:
> I ran into the crash a while ago in the CI. See also
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83562 .

That bug report shows that GCC does not properly implement thread_local on 
MinGW 32-bit over 8 years after the publication of the standard and over 4 
years after the feature became available on other platforms.

I am proposing we make the C++11 thread_local feature mandatory and stop 
supporting any compilers that fail to support it. 

That would exclude GCC on MinGW 32-bit. 32-bit Windows GCC-compatible-ABI 
support would be provided by Clang.

If this proposal seems acceptable, we need to see if it is technically 
feasible: can Clang/MinGW compile our codebase? And how does one go about 
installing it?

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel System Software Products