[Modules TS] Added module re-export support.

This implements [dcl.modules.export] from the C++ Modules TS, which lets a module re-export another module with the "export import" syntax.
Differential Revision: https://reviews.llvm.org/D40270

llvm-svn: 318744
diff --git a/clang/lib/Parse/ParseObjc.cpp b/clang/lib/Parse/ParseObjc.cpp
index edf1da1..fb8624a 100644
--- a/clang/lib/Parse/ParseObjc.cpp
+++ b/clang/lib/Parse/ParseObjc.cpp
@@ -81,8 +81,10 @@
     SingleDecl = ParseObjCPropertyDynamic(AtLoc);
     break;
   case tok::objc_import:
-    if (getLangOpts().Modules || getLangOpts().DebuggerSupport)
-      return ParseModuleImport(AtLoc);
+    if (getLangOpts().Modules || getLangOpts().DebuggerSupport) {
+      SingleDecl = ParseModuleImport(AtLoc);
+      break;
+    }
     Diag(AtLoc, diag::err_atimport);
     SkipUntil(tok::semi);
     return Actions.ConvertDeclToDeclGroup(nullptr);