PATCH: Check TLS for libgcc

[Paolo Bonzini]

> Luckily, we can use GCC_CHECK_TLS for the native compiler of the
> native target.  Even if the build compiler doesn't support TLS, it
> won't be a problem.  The stage 2 and stage 3 libgcc will have proper
> TLS support if the stage 2 and stage 3 compilers do supprot TLS at
> run-time. During stage 3, the compiler checked by GCC_CHECK_TLS in
> gcc in this case is the stage 2 compiler, which should have the
> identical features as the stage 3 compiler, which will be used to
> compile stage 3 libgcc. So libgcc can use auto-host.h in gcc to check
> if TLS can be used for the native compiler of the native target.

Actually, neither your patch nor my alternative proposal will work if 
--disable-bootstrap is used.  The test would then be done on the build 
compiler ("stage0").

Paolo