Revert r280035 (and followups r280057, r280085), it caused PR30195

llvm-svn: 280091
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index 0bc4680..e58e3f7 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -546,13 +546,7 @@
     return false;
   } else if (getLangOpts().getCompilingModule() ==
              LangOptions::CMK_ModuleInterface) {
-    // FIXME: We avoid providing this diagnostic when generating an object file
-    // from an existing PCM file. This is not a good way to detect this
-    // condition; we should provide a mechanism to indicate whether we've
-    // already parsed a declaration in this translation unit and avoid calling
-    // ParseFirstTopLevelDecl in that case.
-    if (Actions.TUKind == TU_Module)
-      Diag(Tok, diag::err_expected_module_interface_decl);
+    Diag(Tok, diag::err_expected_module_interface_decl);
   }
 
   // C11 6.9p1 says translation units must have at least one top-level