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, 8 insertions, 0 deletions

diff --git a/objectivec/GPBUnknownField.m b/objectivec/GPBUnknownField.m
index 0e29bde5..30efe756 100644
--- a/objectivec/GPBUnknownField.m
+++ b/objectivec/GPBUnknownField.m
@@ -67,6 +67,12 @@
   [super dealloc];
 }
 
+// Direct access is use for speed, to avoid even internally declaring things
+// read/write, etc. The warning is enabled in the project to ensure code calling
+// protos can turn on -Wdirect-ivar-access without issues.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdirect-ivar-access"
+
 - (id)copyWithZone:(NSZone *)zone {
   GPBUnknownField *result =
       [[GPBUnknownField allocWithZone:zone] initWithNumber:number_];
@@ -323,4 +329,6 @@
   }
 }
 
+#pragma clang diagnostic pop
+
 @end