PLATFORM(IOS) should come before __MAC_OS_X_VERSION_MIN_REQUIRED
https://bugs.webkit.org/show_bug.cgi?id=108101

Reviewed by Benjamin Poulain.

Since iOS does not define __MAC_OS_X_VERSION_MIN_REQUIRED, any usage of
__MAC_OS_X_VERSION_MIN_REQUIRED should be after a PLATFORM(IOS) check.

Source/WebCore:

* platform/mac/WebCoreSystemInterface.h:
* platform/mac/WebCoreSystemInterface.mm:

Source/WebKit/mac:

* WebCoreSupport/WebSystemInterface.mm:
(InitWebCoreSystemInterface):

Source/WebKit2:

* WebProcess/WebCoreSupport/mac/WebSystemInterface.mm:
(InitWebCoreSystemInterface):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141025 268f45cc-cd09-0410-ab3c-d52691b4dbfc