https://bugs.webkit.org/show_bug.cgi?id=170385 fixed a warning about Mac OS build sleight of hand for libwebrtc by telling the linker that release builds of WebKit and WebCore will not be placed in a dyld shared cache. However on some devices this is desirable. Since we only do the sleight of hand on macosx restrict the flag to macosx.
<rdar://problem/50675982>
Created attachment 370471 [details] patch
Thanks Dan. http://trac.webkit.org/projects/webkit/changeset/245717