OpenMP: Fix reverse offload GOMP_TARGET_REV IFN corner cases [PR107236]

OpenMP: Fix reverse offload GOMP_TARGET_REV IFN corner cases [PR107236]

For 'target parallel' and similarly nested directives, cgraph_node's
calls_declare_variant_alt was not set in the parent region node but in
cfun->decl. Hence, pass_omp_device_lower did not process handle the
internal function GOMP_TARGET_REV. - Solution is to set it to the
DECL_CONTEXT, which is set in adjust_context_and_scope.

The cgraph_node::create_clone issue is exposed with -O2 for the existing
libgomp.fortran/reverse-offload-1.f90.

	PR middle-end/107236

gcc/ChangeLog:
	* omp-expand.cc (expand_omp_target): Set calls_declare_variant_alt
	in DECL_CONTEXT and not to cfun->decl.
	* cgraphclones.cc (cgraph_node::create_clone): Copy also the
	node's calls_declare_variant_alt value.

gcc/testsuite/ChangeLog:
	* gfortran.dg/gomp/target-device-ancestor-6.f90: New test.