Add more warnings to for the ObjC runtime build

Working on https://github.com/google/protobuf/issues/1599, specifically:
- Turn on more warnings that the Xcode UI calls out with individual controls.
- Manually add:
  -Wundef
  -Wswitch-enum
- Manually add and then diable in the unittests because of XCTest's headers:
  -Wreserved-id-macro
  -Wdocumentation-unknown-command
- Manually add -Wdirect-ivar-access, but disable it for the unittests and in
  the library code (via #pragmas to suppress it). This is done so proto users
  can enable the warning.

1 files changed, 3 insertions, 0 deletions

diff --git a/objectivec/GPBMessage_PackagePrivate.h b/objectivec/GPBMessage_PackagePrivate.h
index 478db2cf..ff3cd6eb 100644
--- a/objectivec/GPBMessage_PackagePrivate.h
+++ b/objectivec/GPBMessage_PackagePrivate.h
@@ -110,9 +110,12 @@ CF_EXTERN_C_BEGIN
 
 // Call this before using the readOnlySemaphore_. This ensures it is created only once.
 NS_INLINE void GPBPrepareReadOnlySemaphore(GPBMessage *self) {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdirect-ivar-access"
   dispatch_once(&self->readOnlySemaphoreCreationOnce_, ^{
     self->readOnlySemaphore_ = dispatch_semaphore_create(1);
   });
+#pragma clang diagnostic pop
 }
 
 // Returns a new instance that was automatically created by |autocreator| for