openmp: Add OpenMP _BitInt support [PR113409]

The following patch adds support for _BitInt iterators of OpenMP canonical
loops (with the preexisting limitation that when not using compile time
static scheduling the iterators in the library are at most unsigned long long
or signed long, so one can't in the runtime/dynamic/guided etc. cases iterate
more than what those types can represent, like is the case of e.g. __int128
iterators too) and the testcase also covers linear/reduction clauses for them.

2024-01-17  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/113409
	* omp-general.cc (omp_adjust_for_condition): Handle BITINT_TYPE like
	INTEGER_TYPE.
	(omp_extract_for_data): Use build_bitint_type rather than
	build_nonstandard_integer_type if either iter_type or loop->v type
	is BITINT_TYPE.
	* omp-expand.cc (expand_omp_for_generic,
	expand_omp_taskloop_for_outer, expand_omp_taskloop_for_inner): Handle
	BITINT_TYPE like INTEGER_TYPE.

	* testsuite/libgomp.c/bitint-1.c: New test.