[pch] Honour -fallow-pch-with-compiler-errors for overall compilation status

Previously we would emit a PCH with errors, but fail the overall
compilation. If run using the driver, that would result in removing the
just-produced PCH. Instead, we should have the compilation result match
whether we were able to emit the PCH.

Differential Revision: https://reviews.llvm.org/D77159

rdar://61110294

Author: benlangmuir

clang/lib/Serialization/GeneratePCH.cpp

@@ -57,6 +57,11 @@ void PCHGenerator::HandleTranslationUnit(ASTContext &Ctx) {
     }
   }
 
+  // Errors that do not prevent the PCH from being written should not cause the
+  // overall compilation to fail either.
+  if (AllowASTWithErrors)
+    PP.getDiagnostics().getClient()->clear();
+
   // Emit the PCH file to the Buffer.
   assert(SemaPtr && "No Sema?");
   Buffer->Signature =

clang/test/Index/pch-with-errors.c

@@ -42,3 +42,6 @@ void foo(void) {
 
 // RUN: not c-index-test -write-pch %t.pch foobar.c 2>&1 | FileCheck -check-prefix=NONEXISTENT %s
 // NONEXISTENT: Unable to load translation unit
+
+// RUN: %clang -x c-header %s -o %t-clang.h.pch -Xclang -detailed-preprocessing-record -Xclang -fallow-pch-with-compiler-errors
+// RUN: c-index-test -index-file %s -include %t-clang.h -Xclang -detailed-preprocessing-record | FileCheck -check-prefix=CHECK-INDEX %s