[PCH] Mark a PCH file with a flag to indicate if the serialized AST had
compiler errors or not.

-Control whether ASTReader should reject such a PCH by a boolean flag at ASTReader's creation time.
By default, such a PCH file will be rejected with an error when trying to load it.

[libclang] Allow clang_saveTranslationUnit to create a PCH file even if compiler errors
occurred.
-Have libclang API calls accept a PCH that had compiler errors.

The general idea is that we want libclang to stay functional even if a PCH had a compiler error.
rdar://10976363.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@152192 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/libclang/CIndex.cpp b/tools/libclang/CIndex.cpp
index 3b02595..7e4a1ed 100644
--- a/tools/libclang/CIndex.cpp
+++ b/tools/libclang/CIndex.cpp
@@ -2438,7 +2438,9 @@
   IntrusiveRefCntPtr<DiagnosticsEngine> Diags;
   ASTUnit *TU = ASTUnit::LoadFromASTFile(ast_filename, Diags, FileSystemOpts,
                                   CXXIdx->getOnlyLocalDecls(),
-                                  0, 0, true);
+                                  0, 0,
+                                  /*CaptureDiagnostics=*/true,
+                                  /*AllowPCHWithCompilerErrors=*/true);
   return MakeCXTranslationUnit(TU);
 }
 
@@ -2575,7 +2577,8 @@
                                  /*RemappedFilesKeepOriginalName=*/true,
                                  PrecompilePreamble,
                                  TUKind,
-                                 CacheCodeCompetionResults));
+                                 CacheCodeCompetionResults,
+                                 /*AllowPCHWithCompilerErrors=*/true));
 
   if (NumErrors != Diags->getClient()->getNumErrors()) {
     // Make sure to check that 'Unit' is non-NULL.