[OpenMP] Fix performance issue from 376.kdtree

This change improves the performance of 376.kdtree by giving the compiler an
opportunity to do inlining and other optimizations for the call path,
__kmpc_omp_task_complete_if0()->__kmp_task_finish(), which is one of the hot
paths in the program; some functions in kmp_taskdeps.cpp were moved to the new
header file, kmp_taskdeps.h to achieve this.

Patch by Hansang Bae

Differential Revision: https://reviews.llvm.org/D51889

llvm-svn: 343138