[flang] Fix call to CHECK() on erroneous subroutine declaration

When processing declarations in resolve-names.cpp, we were returning a
symbol that had SubprogramName details to PushSubprogramScope(), which
expects a symbol with Subprogram details.

I adjusted the code and added a test.

Differential Revision: https://reviews.llvm.org/D89829

Author: psteinfeld

flang/lib/Semantics/resolve-names.cpp

@@ -3048,7 +3048,8 @@ Symbol *SubprogramVisitor::GetSpecificFromGeneric(const parser::Name &name) {
         details->set_specific(Resolve(name, *specific));
       } else if (isGeneric()) {
         SayAlreadyDeclared(name, *specific);
-      } else if (!specific->has<SubprogramDetails>()) {
+      }
+      if (!specific->has<SubprogramDetails>()) {
         specific->set_details(SubprogramDetails{});
       }
       return specific;

flang/test/Semantics/resolve19.f90

@@ -22,3 +22,14 @@ subroutine s(x)
     end subroutine
   end interface
 end module
+
+module m3
+  interface s
+    subroutine s
+    end
+  end interface
+contains
+  !ERROR: 's' is already declared in this scoping unit
+  subroutine s
+  end subroutine
+end