Add a cc1 flag for setting the existing Preprocessor option 'AllowPCHWithCompilerErrors'.

llvm-svn: 296306
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 2ef9639..59db36d 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2296,6 +2296,7 @@
   Opts.UsePredefines = !Args.hasArg(OPT_undef);
   Opts.DetailedRecord = Args.hasArg(OPT_detailed_preprocessing_record);
   Opts.DisablePCHValidation = Args.hasArg(OPT_fno_validate_pch);
+  Opts.AllowPCHWithCompilerErrors = Args.hasArg(OPT_fallow_pch_with_errors);
 
   Opts.DumpDeserializedPCHDecls = Args.hasArg(OPT_dump_deserialized_pch_decls);
   for (const Arg *A : Args.filtered(OPT_error_on_deserialized_pch_decl))