Introduce KMP_COMPILER_ICX macro to represent compilation with oneAPI
compiler.
Fixup flag detection and compiler ID detection in CMake. Older CMake's
detect IntelLLVM as Clang.
Fix compiler warnings.
Fixup many of the tests to have non-empty parallel regions as they are
elided by oneAPI compiler.
Fix the newly-added tests to use %python substitution in order to use
the correct path to Python interpreter. Otherwise, they fail on NetBSD
where there is no 'python', just 'pythonX.Y'.
Differential Revision: https://reviews.llvm.org/D56048
llvm-svn: 350001