CONFIGURE: fix undefined reference to `g_type_init'

These two assignments have no place here and will overwrite the
previous COMMON_LIBS="$COMMON_LIBS -lgmodule-2.0 -lgobject-2.0".
This can lead to build failure during linking stage depending on
the chosen configure options.
Merge pull request #580 from hasufell/master

Build failure: fix undefined reference to `g_type_init'