Fix Mac build after r24676.

BUG=v8:3638
LOG=n
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/659253002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24679 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

build/standalone.gypi

@@ -136,8 +136,13 @@
     'configurations': {
       'DebugBaseCommon': {
         'cflags': [ '-g', '-O0' ],
-        'defines': [
-          '_GLIBCXX_DEBUG'
+        'conditions': [
+          ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd" or \
+            OS=="qnx"', {
+            'defines': [
+              '_GLIBCXX_DEBUG'
+            ],
+          }],
         ],
       },
       'Optdebug': {