[libclang] If displayDiagnostics is set (when calling clang_createIndex), make sure to
output the errors that occurred even if we did not get an AST (e.g. because the
PCH failed to load).

Also honor displayDiagnostics in clang_indexSourceFile().

rdar://11203489

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154472 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/libclang/Indexing.cpp b/tools/libclang/Indexing.cpp
index 6ece548..e660c4d 100644
--- a/tools/libclang/Indexing.cpp
+++ b/tools/libclang/Indexing.cpp
@@ -388,7 +388,8 @@
     }
   }
 
-  Unit = ASTUnit::LoadFromCompilerInvocationAction(CInvok.getPtr(), Diags,
+  DiagnosticErrorTrap DiagTrap(*Diags);
+  bool Success = ASTUnit::LoadFromCompilerInvocationAction(CInvok.getPtr(), Diags,
                                                        IndexAction.get(),
                                                        Unit,
                                                        Persistent,
@@ -397,7 +398,10 @@
                                                     /*CaptureDiagnostics=*/true,
                                                        PrecompilePreamble,
                                                     CacheCodeCompletionResults);
-  if (!Unit)
+  if (DiagTrap.hasErrorOccurred() && CXXIdx->getDisplayDiagnostics())
+    printDiagsToStderr(Unit);
+
+  if (!Success)
     return;
 
   if (out_TU)