libgloss: move to ../config/multi.m4 for multilib logic

libgloss: move to ../config/multi.m4 for multilib logic

The current libgloss multilib logic is almost exactly the same as the
config/multi.m4, and the differences should be minor, so switch over
to that to delete custom logic on ourside.

The insertions here look larger and that's because none of the scripts
were declaring --enable-multilib explicitly even though they checked the
flag and changed behavior.