openmp: Also implicitly mark as declare target to functions mentioned in target regions

openmp: Also implicitly mark as declare target to functions mentioned in target regions

OpenMP 5.0 also specifies that functions referenced from target regions
(except for target regions with device(ancestor:)) are also implicitly declare target to.

This patch implements that.

2020-05-14  Jakub Jelinek  <jakub@redhat.com>

	* function.h (struct function): Add has_omp_target bit.
	* omp-offload.c (omp_discover_declare_target_fn_r): New function,
	old renamed to ...
	(omp_discover_declare_target_tgt_fn_r): ... this.
	(omp_discover_declare_target_var_r): Call
	omp_discover_declare_target_tgt_fn_r instead of
	omp_discover_declare_target_fn_r.
	(omp_discover_implicit_declare_target): Also queue functions with
	has_omp_target bit set, for those walk with
	omp_discover_declare_target_fn_r, for declare target to functions
	walk with omp_discover_declare_target_tgt_fn_r.
gcc/c/
	* c-parser.c (c_parser_omp_target): Set cfun->has_omp_target.
gcc/cp/
	* cp-gimplify.c (cp_genericize_r): Set cfun->has_omp_target.
gcc/fortran/
	* trans-openmp.c: Include function.h.
	(gfc_trans_omp_target): Set cfun->has_omp_target.
libgomp/
	* testsuite/libgomp.c-c++-common/target-40.c: New test.