os: check for GALLIUM_PROCESS_NAME to override os_get_process_name()
os: check for GALLIUM_PROCESS_NAME to override os_get_process_name()

Useful for debugging and for glretrace.

Reviewed-by: Charmaine Lee <67ce69700661ea856134ddb10419a330e5f037d7@vmware.com>
Reviewed-by: José Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler