Disable deprecation warnings when -Werror is enabled. (#609)

CMakeLists.txt

@@ -143,6 +143,10 @@ else()
   # Disable warnings regarding deprecated parts of the library while building
   # and testing those parts of the library.
   add_cxx_compiler_flag(-Wno-deprecated-declarations)
+  # Disable deprecation warnings for release builds (when -Werror is enabled).
+  add_cxx_compiler_flag(-Wno-deprecated RELEASE)
+  add_cxx_compiler_flag(-Wno-deprecated RELWITHDEBINFO)
+  add_cxx_compiler_flag(-Wno-deprecated MINSIZEREL)
   if (NOT BENCHMARK_ENABLE_EXCEPTIONS)
     add_cxx_compiler_flag(-fno-exceptions)
   endif()

include/benchmark/benchmark.h

@@ -226,7 +226,7 @@ BENCHMARK(BM_test)->Unit(benchmark::kMillisecond);
 #define BENCHMARK_INTERNAL_TOSTRING2(x) #x
 #define BENCHMARK_INTERNAL_TOSTRING(x) BENCHMARK_INTERNAL_TOSTRING2(x)
 
-#if defined(__GNUC__)
+#if defined(__GNUC__) || defined(__clang__)
 #define BENCHMARK_BUILTIN_EXPECT(x, y) __builtin_expect(x, y)
 #define BENCHMARK_DEPRECATED_MSG(msg) __attribute__((deprecated(msg)))
 #else