re PR middle-end/79236 (Many libgomp tests fail if configured with --enable-offload...

re PR middle-end/79236 (Many libgomp tests fail if configured with --enable-offload-targets=nvptx-none but NVidia HW or libcuda.so.1 unavailable)

	PR middle-end/79236
	* omp-low.c (struct omp_context): Add simt_stmt field.
	(scan_omp_for): Return omp_context *.
	(scan_omp_simd): Set simt_stmt on the non-_simt_ SIMD
	context to the _simt_ SIMD stmt.
	(lower_omp_for): For combined SIMD with sibling _simt_
	SIMD, make sure to use the same decls in _looptemp_
	clauses as in the sibling.

From-SVN: r244924