Attempt to fix build

FAILED: Source/JavaScriptCore/CMakeFiles/LLIntOffsetsExtractor.dir/llint/LLIntOffsetsExtractor.cpp.o
...
In file included from /wrkdirs/usr/ports/www/webkit2-gtk3/work/webkitgtk-2.20.0/Source/JavaScriptCore/llint/LLIntOffsetsExtractor.cpp:28:
In file included from /wrkdirs/usr/ports/www/webkit2-gtk3/work/webkitgtk-2.20.0/Source/JavaScriptCore/bytecode/ArrayProfile.h:28:
In file included from /wrkdirs/usr/ports/www/webkit2-gtk3/work/webkitgtk-2.20.0/Source/JavaScriptCore/runtime/ConcurrentJSLock.h:28:
In file included from /wrkdirs/usr/ports/www/webkit2-gtk3/work/webkitgtk-2.20.0/Source/JavaScriptCore/heap/DeferGC.h:29:
In file included from /wrkdirs/usr/ports/www/webkit2-gtk3/work/webkitgtk-2.20.0/Source/JavaScriptCore/heap/Heap.h:33:
In file included from /wrkdirs/usr/ports/www/webkit2-gtk3/work/webkitgtk-2.20.0/Source/JavaScriptCore/heap/HeapFinalizerCallback.h:28:
/wrkdirs/usr/ports/www/webkit2-gtk3/work/webkitgtk-2.20.0/Source/JavaScriptCore/API/JSHeapFinalizerPrivate.h:29:10: fatal error: 'JavaScriptCore/JSContextRef.h' file not found

Submitted by: tcberner@
Reported by: pkg-fallout