Contrary my previous claim in r238564, ENABLE_SEPARATED_WX_HEAP needs to be defined in Platform.h because it is also needed in WebCore for the CSS JIT. Also contrary to my previous claim, ENABLE(FAST_JIT_PERMISSIONS) is defined for WebCore (and other projects) as well as JSC. Hence, there's no reason why ENABLE_SEPARATED_WX_HEAP cannot be defined in Platform.h.
Created attachment 355927 [details]
Thanks for the review. Landed in r238650: <http://trac.webkit.org/r238650>.