[flang] Add more qualification when creating names for compiler-generated USEs

[klausler]

Summary

When generic resolution finds its specific procedure in a module,
and that specific procedure is not use-associated into the local scope
(perhaps because it was PRIVATE, perhaps because the generic was
use-associated with ONLY:), we create a new use-association with
a renaming. The name constructed for this renaming needs to be
additionally qualified with the module name of the specific procedure
in order to avoid clashing with another specific of the same name
that may have previously been use-associated in the same way from
a distinct module.

[kiranchandramohan]

Change LGTM. It fixes the issue reported in https://github.com/llvm/llvm-project/issues/55841 and also the related issue seen in cam4 & pop2 spec benchmarks. Thanks.

flang/lib/Semantics/expression.cpp

if (auto iter{scope.find(specific.name())}; iter != scope.end()) {
             (usedGeneric && usedGeneric->specific() == &specific)) {
           return specific;
         }
       }
     }
     // Create a renaming USE of the specific procedure.
     auto rename{context_.SaveTempName(
         used->symbol().owner().GetName().value().ToString() + "$" +
+        specific.owner().GetName().value().ToString() + "$" +
         specific.name().ToString())};
     return *const_cast<semantics::Scope &>(scope)
                 .try_emplace(rename, specific.attrs(),
                     semantics::UseDetails{rename, specific})
                 .first->second;
   } else {
     return specific;
   }

flang/test/Semantics/modfile39.f90

  contains
   subroutine s(a)
     real :: a(gen(1))
   end subroutine
 end module
 !Expect: m2.mod
 !module m2
 !use m1,only:gen
-!use m1,only:m1$priv=>priv
-!private::m1$priv
+!use m1,only:m1$m1$priv=>priv
+!private::m1$m1$priv
 !contains
 !subroutine s(a)
-!real(4)::a(1_8:int(m1$priv(1_4),kind=8))
+!real(4)::a(1_8:int(m1$m1$priv(1_4),kind=8))
 !end
 !end
 
 use m2
 end