src,macos: fix mutually exclusive flags

If IPHONEOS_DEPLOYMENT_TARGET is specified, don't append
MACOSX_DEPLOYMENT_TARGET flags.

Author: shawwn

gyp/xcode_emulation.py

@@ -525,7 +525,6 @@ def _XcodeSdkPath(self, sdk_root):
     return XcodeSettings._sdk_path_cache[sdk_root]
 
   def _AppendPlatformVersionMinFlags(self, lst):
-    self._Appendf(lst, 'MACOSX_DEPLOYMENT_TARGET', '-mmacosx-version-min=%s')
     if 'IPHONEOS_DEPLOYMENT_TARGET' in self._Settings():
       # TODO: Implement this better?
       sdk_path_basename = os.path.basename(self._SdkPath())
@@ -535,6 +534,8 @@ def _AppendPlatformVersionMinFlags(self, lst):
       else:
         self._Appendf(lst, 'IPHONEOS_DEPLOYMENT_TARGET',
                       '-miphoneos-version-min=%s')
+    else:
+      self._Appendf(lst, 'MACOSX_DEPLOYMENT_TARGET', '-mmacosx-version-min=%s')
 
   def GetCflags(self, configname, arch=None):
     """Returns flags that need to be added to .c, .cc, .m, and .mm