OpenMP: Fix 'omp declare target' handling for vars [PR99509]

For variables with 'declare target' attribute,
varpool_node::get_create marks variables as offload; however,
if the node already exists, it is not updated. C/C++ may tag
decl with 'declare target implicit', which may only be after
varpool creation turned into 'declare target' or 'declare target link';
in this case, the tagging has to happen in the FE.

gcc/c/ChangeLog:

	PR c++/99509
	* c-decl.c (finish_decl): For 'omp declare target implicit' vars,
	ensure that the varpool node is marked as offloadable.

gcc/cp/ChangeLog:

	PR c++/99509
	* decl.c (cp_finish_decl): For 'omp declare target implicit' vars,
	ensure that the varpool node is marked as offloadable.

libgomp/ChangeLog:

	PR c++/99509
	* testsuite/libgomp.c-c++-common/declare_target-1.c: New test.

1 files changed, 19 insertions, 3 deletions

diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index b559ed5..3b2241b 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -58,6 +58,9 @@ along with GCC; see the file COPYING3.  If not see
 #include "c-family/name-hint.h"
 #include "c-family/known-headers.h"
 #include "c-family/c-spellcheck.h"
+#include "context.h"  /* For 'g'.  */
+#include "omp-general.h"
+#include "omp-offload.h"  /* For offload_vars.  */
 
 #include "tree-pretty-print.h"
 
@@ -5658,9 +5661,22 @@ finish_decl (tree decl, location_t init_loc, tree init,
 				  DECL_ATTRIBUTES (decl))
 	       && !lookup_attribute ("omp declare target link",
 				     DECL_ATTRIBUTES (decl)))
-	DECL_ATTRIBUTES (decl)
-	  = tree_cons (get_identifier ("omp declare target"),
-		       NULL_TREE, DECL_ATTRIBUTES (decl));
+	{
+	  DECL_ATTRIBUTES (decl)
+	    = tree_cons (get_identifier ("omp declare target"),
+			 NULL_TREE, DECL_ATTRIBUTES (decl));
+	    symtab_node *node = symtab_node::get (decl);
+	    if (node != NULL)
+	      {
+		node->offloadable = 1;
+		if (ENABLE_OFFLOADING)
+		  {
+		    g->have_offload = true;
+		    if (is_a <varpool_node *> (node))
+		      vec_safe_push (offload_vars, decl);
+		  }
+	      }
+	}
     }
 
   /* This is the last point we can lower alignment so give the target the