openmp: Implicitly discover declare target for variants of declare variant calls

openmp: Implicitly discover declare target for variants of declare variant calls

This marks all variants of declare variant also declare target if the base
functions are called directly in target regions or declare target functions.

2020-10-28  Jakub Jelinek  <jakub@redhat.com>

gcc/
	* omp-offload.c (omp_declare_target_tgt_fn_r): Handle direct calls to
	declare variant base functions.
libgomp/
	* testsuite/libgomp.c/target-42.c: New test.