omp-low.c split

[Cesar Philippidis]

What's the plan to split omp-low.c into multiple files? Right now,
omp-low.c contains code to lower and expand OpenMP and OpenACC. At least
for the OpenACC transforms, we made an effort to keep the changes in
omp-low.c target-independent. Is goal to break omp-low.c into separate
lowering, expansion and target/offloading-specific files?

Is there a timeline for it? The major pending OpenACC changes involve
the tile clause and routines. Most of the routine changes happen in the
FEs, we do preform some error handling in omp-low.c.

Cesar