[OPENMP] Bug fixes and improvements.
1. Fixed constructor of shared clause.
2. Some macros for clauses processing are replaced by private template methods.
3. Additional checks in sema analysis of OpenMP clauses.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191265 91177308-0d34-0410-b5e6-96231b3b80d8