glapi: fix _glapi_get_proc_address() for mangled function names
glapi: fix _glapi_get_proc_address() for mangled function names

In the dispatch table, all functions are stored without the "m" prefix.
Modify code so that OSMesaGetProcAddress works both with gl and mgl
prefixes. Similar to
https://lists.freedesktop.org/archives/mesa-dev/2015-September/095251.html

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94994
Cc: "11.1 11.2" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler