[flang] Silence a bogus warning (#69799)

A recent fix (#66232) to
interpret a hitherto unknown name whose first appearance is as the
target of a procedure pointer initializer as an external procedure has
led to some inapproprite warning messages if the name is later defined
as an external subroutine ("X was already declared as an external").

Ensure that the EXTERNAL attribute is correctly noted as being implicit,
and that it's okay that neither the Subroutine nor Function flag has yet
been set for the implicit external.

flang/lib/Semantics/resolve-names.cpp

@@ -4191,18 +4191,23 @@ bool SubprogramVisitor::HandlePreviousCalls(
     // ENTRY's name.  We have to replace that symbol in situ to avoid the
     // obligation to rewrite symbol pointers in the parse tree.
     if (!symbol.test(subpFlag)) {
+      auto other{subpFlag == Symbol::Flag::Subroutine
+              ? Symbol::Flag::Function
+              : Symbol::Flag::Subroutine};
       // External statements issue an explicit EXTERNAL attribute.
       if (symbol.attrs().test(Attr::EXTERNAL) &&
           !symbol.implicitAttrs().test(Attr::EXTERNAL)) {
         // Warn if external statement previously declared.
         Say(name,
             "EXTERNAL attribute was already specified on '%s'"_warn_en_US);
-      } else {
+      } else if (symbol.test(other)) {
         Say2(name,
             subpFlag == Symbol::Flag::Function
                 ? "'%s' was previously called as a subroutine"_err_en_US
                 : "'%s' was previously called as a function"_err_en_US,
             symbol, "Previous call of '%s'"_en_US);
+      } else {
+        symbol.set(subpFlag);
       }
     }
     EntityDetails entity;
@@ -8163,6 +8168,7 @@ bool ResolveNamesVisitor::Pre(const parser::PointerAssignmentStmt &x) {
       // Unknown target of procedure pointer must be an external procedure
       Symbol &symbol{MakeSymbol(
           context().globalScope(), name->source, Attrs{Attr::EXTERNAL})};
+      symbol.implicitAttrs().set(Attr::EXTERNAL);
       Resolve(*name, symbol);
       ConvertToProcEntity(symbol);
       return false;