Add a flag to disable "duplicate definition of category" warnings

[ahatanak]

Fix clang/test/Misc/warning-flags.c

[vsapsai]

As long as there are no other failing tests, looks good to me.

clang/include/clang/Basic/DiagnosticCommonKinds.td

 
 def warn_slh_does_not_support_asm_goto : Warning<
   "speculative load hardening does not protect functions with asm goto">,
   InGroup<DiagGroup<"slh-asm-goto">>;
 }
 
 // Sema && Serialization
 def warn_dup_category_def : Warning<
-  "duplicate definition of category %1 on interface %0">;
+  "duplicate definition of category %1 on interface %0">,
+  InGroup<DiagGroup<"objc-duplicate-category-definition">>;
 
 // Targets
 
 def err_target_unknown_triple : Error<
   "unknown target triple '%0'">;
 def err_target_unknown_cpu : Error<"unknown target CPU '%0'">;
 def note_valid_options : Note<"valid target CPU values are: %0">;
 def err_target_unsupported_cpu_for_micromips : Error<

clang/test/SemaObjC/check-dup-objc-decls-1.m

 // RUN: %clang_cc1 -fsyntax-only -verify -Wno-objc-root-class %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-objc-root-class -Wno-objc-duplicate-category-definition -DIGNORE_DUP_CAT %s
 
 @interface Foo // expected-note {{previous definition is here}}
 @end
 
 float Foo;  // expected-error {{redefinition of 'Foo' as different kind of symbol}}
 
 @class Bar;  // expected-note {{previous definition is here}}
 

 @protocol PP<Q> @end  // expected-warning {{duplicate protocol definition of 'PP'}}
 
 @protocol DP<P> @end
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wduplicate-protocol"
 @protocol DP<Q> @end
 #pragma clang diagnostic pop
 
-@interface A(Cat)<P> @end // expected-note {{previous definition is here}}
-@interface A(Cat)<Q> @end // expected-warning {{duplicate definition of category 'Cat' on interface 'A'}}
+@interface A(Cat)<P> @end
+@interface A(Cat)<Q> @end
+
+#ifndef IGNORE_DUP_CAT
+// expected-note@-4 {{previous definition is here}}
+// expected-warning@-4 {{duplicate definition of category 'Cat' on interface 'A'}}
+#endif
 
 // rdar 7626768
 @class NSString;
 NSString * TestBaz;  // expected-note {{previous definition is here}}
 NSString * const TestBaz;  // expected-error {{redefinition of 'TestBaz' with a different type}}