st/wgl: add some mutex checking code
st/wgl: add some mutex checking code

This would have caught the locking bug that was fixed in the earlier
"st/wgl: fix locking issue in stw_st_framebuffer_present_locked()"
patch.

v2: minor coding style changes by Brian.

Reviewed-by: Sinclair Yeh <326bbc75ae5821d6c8d1817b260a4d8d0fdf1f63@vmware.com>
Reviewed-by: Charmaine Lee <67ce69700661ea856134ddb10419a330e5f037d7@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler