[clang] Disable assertion that can "easily happen"

[JDevlieghere]

Summary

Disable the assertion for getting a module ID for non-local,
non-imported module. According to the FIXME this can "easily happen" and
indeed, we're hitting this assertion regularly. Disable it until it can
be properly investigated.

rdar://99352728

[Bigcheese]

lgtm.

clang/lib/Serialization/ASTWriter.cpp

if (Top != WritingModule &&
       (getLangOpts().CompilingPCH ||
        !Top->fullModuleNameIs(StringRef(getLangOpts().CurrentModule))))
     return 0;
 
   return SubmoduleIDs[Mod] = NextSubmoduleID++;
 }
 
 unsigned ASTWriter::getSubmoduleID(Module *Mod) {
+  unsigned ID = getLocalOrImportedSubmoduleID(Mod);
   // FIXME: This can easily happen, if we have a reference to a submodule that
   // did not result in us loading a module file for that submodule. For
   // instance, a cross-top-level-module 'conflict' declaration will hit this.
-  unsigned ID = getLocalOrImportedSubmoduleID(Mod);
-  assert((ID || !Mod) &&
-         "asked for module ID for non-local, non-imported module");
+  // assert((ID || !Mod) &&
+  //        "asked for module ID for non-local, non-imported module");
   return ID;
 }
 
 /// Compute the number of modules within the given tree (including the
 /// given module).
 static unsigned getNumberOfModules(Module *Mod) {
   unsigned ChildModules = 0;
   for (auto Sub = Mod->submodule_begin(), SubEnd = Mod->submodule_end();