Properly check GLX_INDIRECT_RENDERING in glapi/tests/check_table

Properly check GLX_INDIRECT_RENDERING in glapi/tests/check_table

Actually use $DEFINES, so we can see if GLX_INDIRECT_RENDERING is defined

If GLX_INDIRECT_RENDERING is defined,  _GLAPI_SKIP_PROTO_ENTRY_POINTS will
be defined, and libglapi won't contain the 'protocol entry points', so we
should provide stubs in check_table.cpp