openmp: Fix up declare target handling for vars with DECL_LOCAL_DECL_ALIAS [PR102640]

openmp: Fix up declare target handling for vars with DECL_LOCAL_DECL_ALIAS [PR102640]

The introduction of DECL_LOCAL_DECL_ALIAS and push_local_extern_decl_alias
in r11-3699-g4e62aca0e0520e4ed2532f2d8153581190621c1a broke the following
testcase.  The following patch fixes it by treating similarly not just
the variable to or link clause is put on, but also its DECL_LOCAL_DECL_ALIAS
if any.  If it hasn't been created yet, when it is created it will copy
attributes and therefore should get it for free, and as it is an extern,
nothing more than attributes is needed for it.

2021-10-08  Jakub Jelinek  <jakub@redhat.com>

	PR c++/102640
gcc/cp/
	* parser.c (handle_omp_declare_target_clause): New function.
	(cp_parser_omp_declare_target): Use it.
gcc/testsuite/
	* c-c++-common/gomp/pr102640.c: New test.