[PATCH] libgfortran: Replace mutex with rwlock

[Zhu, Lipeng via Fortran]

> libstdc++ implements shared mutex with pthread_rwlock, which can 
> libstdc++ conflict
> with the pthread_rwlock usage in libgcc.  Lipeng, please limit the 
> pthread_rwlock usage in libgcc only when __cplusplus isn't defined.
> 
> 
> --
> H.J.

Thanks for suggestion, send a V2 patch. 

--
Lipeng Zhu