Re-activate the -Wno-deprecated-register flag

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 28e3389b76fe724be78b51b54f52bc61a5c1b274..ec1429366d766e66a9c88686686fd675921769b3 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -4153,23 +4153,17 @@
 
                 # Warns when a const char[] is converted to bool.
                 '-Wstring-conversion',
+
+                # Clang considers the `register` keyword as deprecated, but
+                # e.g. code generated by flex (used in angle) contains that
+                # keyword. http://crbug.com/255186
+                '-Wno-deprecated-register',
               ],
 
               'conditions': [
                 ['clang_xcode==0', {
                   'CC': '$(SOURCE_ROOT)/<(clang_dir)/clang',
                   'LDPLUSPLUS': '$(SOURCE_ROOT)/<(clang_dir)/clang++',
-
-                  'WARNING_CFLAGS': [
-                    # Clang considers the `register` keyword as deprecated, but
-                    # e.g. code generated by flex (used in angle) contains that
-                    # keyword. http://crbug.com/255186
-                    #
-                    # Note: clang as shipped with Xcode is older and does not
-                    # treat the `register` as deprecated and does not define
-                    # this flag, so don't enable it if "clang_xcode" is "1".
-                    '-Wno-deprecated-register',
-                  ],
                 }],
               ],
             }],