implement barrier/critical section for OSX (PosixThreadSupport)

enable Demos/ThreadingDemo for OSX
add cmake build support for VectorAdd_OpenCL for OSX

Demos/VectorAdd_OpenCL/Apple/CMakeLists.txt

@@ -0,0 +1,25 @@
+# AppVectorAdd is a very basic test OpenCL/MiniCL.
+
+IF (APPLE)
+  FIND_LIBRARY(OPENCL_LIBRARY OpenCL DOC "OpenCL lib for OSX")
+  FIND_PATH(OPENCL_INCLUDE_DIR OpenCL/cl.h DOC "Include for OpenCL on OSX")
+ENDIF (APPLE)
+
+
+INCLUDE_DIRECTORIES(
+${BULLET_PHYSICS_SOURCE_DIR}/src 
+)
+
+LINK_LIBRARIES(
+  LinearMath ${OPENCL_LIBRARY}
+)
+
+ADD_EXECUTABLE(AppVectorAdd_Apple
+../MiniCL_VectorAdd.cpp
+../VectorAddKernels.cl
+)
+
+IF (UNIX)
+  TARGET_LINK_LIBRARIES(AppVectorAdd_Apple pthread)
+ENDIF(UNIX)
+