[OpenMP] Add missing __kmpc_critical_with_hint to dllexports

This patch puts the __kmpc_critical_with_hint function in dllexports
and also replaces some OMP_45_ENABLED to OMP_50_ENABLED

Differential Revision: https://reviews.llvm.org/D52380


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@343143 91177308-0d34-0410-b5e6-96231b3b80d8