[OpenMP][FIX] Invalidate the SPMDCompatibilityTracker explicitly

Before SPMDzation it was sufficient to add an incompatible instruction
to the SPMDCompatibilityTracker. However, now adding instructions means
they need guarding. As calls cannot be guarded in general we need to
explicitly prevent SPMD mode.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D115158