[OpenMP] Always inline the OpenMP outlined function

This patch adds the always inline attribute to the outlined functions generated
by OpenMP regions. Because there is only a single instance of this function and
it always has internal linkage it is safe to inline in every instance it is
created. This could potentially lead to performance degredation due to
inflated register counts in the parallel region.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D106799