Use forceinline. Necessary for nvcc to inline small functions within the bitcode library

Summary:
[libomptarget] Use forceinline. Necessary for nvcc to inline small functions within the bitcode library
Suggested in D65836

Reviewers: ABataev, jdoerfert, grokos, gregrodgers

Subscribers: openmp-commits

Tags: #openmp

Differential Revision: https://reviews.llvm.org/D65876

llvm-svn: 368177