[OpenMP] libomp: Update third-party sources of ittnotify client code.

The third-party ittnotify sources updated from https://github.com/intel/ittapi.
Changes applied:
- llvm license aded to all files; initial BSD license saved in LICENSE.txt;
- clang-formatted;
- renamed *.c to *.cpp, similar to what we did with all our sources;
- added #include "kmp_config.h" with definition of INTEL_ITTNOTIFY_PREFIX macro
  into ittnotify_static.cpp.

Differential Revision: https://reviews.llvm.org/D109333