[flang][debug] Improve check for global variable.

When a global variable is used in the OpenMP target region, it is
passed as an argument to the function that implements target region.
But the DeclareOp for this incarnation still have the original name of
the variable. As some of our checks to decide if a variable is global
or nor are based on the name, this can result in a local variable being
treated as global. This PR hardens the check a bit. We now also check
that memory ref is actually `an AddrOfOp` before looking at the name.

Author: abidh

flang/lib/Optimizer/Transforms/AddDebugInfo.cpp

@@ -102,15 +102,15 @@ void AddDebugInfoPass::handleDeclareOp(fir::cg::XDeclareOp declOp,
   if (result.first != fir::NameUniquer::NameKind::VARIABLE)
     return;
   // If this DeclareOp actually represents a global then treat it as such.
-  if (auto global = symbolTable->lookup<fir::GlobalOp>(declOp.getUniqName())) {
-    handleGlobalOp(global, fileAttr, scopeAttr, typeGen, symbolTable, declOp);
-    return;
+  mlir::Operation *defOp = declOp.getMemref().getDefiningOp();
+  if (defOp && llvm::isa<fir::AddrOfOp>(defOp)) {
+    if (auto global =
+            symbolTable->lookup<fir::GlobalOp>(declOp.getUniqName())) {
+      handleGlobalOp(global, fileAttr, scopeAttr, typeGen, symbolTable, declOp);
+      return;
+    }
   }
 
-  // Only accept local variables.
-  if (result.second.procs.empty())
-    return;
-
   // FIXME: There may be cases where an argument is processed a bit before
   // DeclareOp is generated. In that case, DeclareOp may point to an
   // intermediate op and not to BlockArgument.