[Bug driver/20705] -pthread should enable all options required to use pthreads on all platforms

[rth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=20705
Bug 20705 depends on bug 14300, which changed state.

Bug 14300 Summary: -pthread doesn't define _REENTRANT in preprocessor on 
alpha-linux
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=14300

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED