Mac: detect x64 macs

This is needed so WITH_SSE2 is turned on automatically.
Merge pull request #1075 from zeha/mac-x64

Mac: detect x64 macs
add KBDEXT to KEYCODE_TO_VKCODE_APPLE where needed
Merge pull request #1076 from zeha/apple_keycodes

add KBDEXT to KEYCODE_TO_VKCODE_APPLE where needed