fix Snow Leopard compatibility Checking for clang in Xcode bundle seems pointless, command line tools should be installed. Setting the path explicity to avoid fink/macports/homebrew prevents use of locally installed packages like clang and wxwidgets. Realistically using opencl means the minimum OSX version targetable is 10.6. Correct TARGET_SYSROOT check, add required -mmacosx-version-min to linker flags. also using wxwidgets gl component.