[OpenMP] libomp: Usage of TASK_TIED constant inside kmp_gsupport.cpp

The minor code refactorization introduces the TASK_TIED constant inside
kmp_gsupprot.cpp as a replacement for the literal value 1.
The mentioned constant is now used in both kmp_tasking.cpp and
kmp_gsupport.cpp files.

Differential Revision: https://reviews.llvm.org/D110441