Make module use diagnostics refer to the top-level module

[djasper]

Summary

All use declarations need to be directly placed in the top-level module anyway, knowing the submodule doesn't really help. The header that has the offending #include can easily be seen in the diagnostics source location.

[rsmith]

Makes sense -- as dependencies can only be declared on top-level modules, that's what we should be talking about here.

[djasper]

Submitted as r326023.

lib/Lex/ModuleMap.cpp

if (Private) {
     Diags.Report(FilenameLoc, diag::warn_use_of_private_header_outside_module)
         << Filename;
     return;
   }
 
   // We have found a module, but we don't use it.
   if (NotUsed) {
     Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module)
-        << RequestingModule->getFullModuleName() << Filename;
+        << RequestingModule->getTopLevelModule()->Name << Filename;
     return;
   }
 
   if (Excluded || isHeaderInUmbrellaDirs(File))
     return;
 
   // At this point, only non-modular includes remain.
 
   if (LangOpts.ModulesStrictDeclUse) {
     Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module)
-        << RequestingModule->getFullModuleName() << Filename;
+        << RequestingModule->getTopLevelModule()->Name << Filename;
   } else if (RequestingModule && RequestingModuleIsModuleInterface &&
              LangOpts.isCompilingModule()) {
     // Do not diagnose when we are not compiling a module. 
     diag::kind DiagID = RequestingModule->getTopLevelModule()->IsFramework ?
         diag::warn_non_modular_include_in_framework_module :
         diag::warn_non_modular_include_in_module;
     Diags.Report(FilenameLoc, DiagID) << RequestingModule->getFullModuleName()
         << File->getName();

test/Modules/Inputs/declare-use/h.h

 #ifndef H_H
 #define H_H
 #include "c.h"
-#include "d.h" // expected-error {{does not depend on a module exporting}}
+#include "d.h" // expected-error {{module XH does not depend on a module exporting}}
 #include "h1.h"
 const int h1 = aux_h*c*7*d;
 #endif