qemu: build using clang
qemu: build using clang

Inline asm and global register variable handling in
darwin11-llvm-gcc-4.2 is not very reliable (for example of a bug, see:
<https://plus.google.com/108138837678270193032/posts/Cc22ZeZxmTm>). So
it's recommended to use clang to build qemu instead.

Signed-off-by: Eduardo Habkost <50373d7c08ceadf576dd7dca718012445b677ce6@raisama.net>

FelixZhang00/rudix,FelixZhang00/rudix,rudix-mac/rudix,FelixZhang00/rudix,FelixZhang00/rudix,rudix-mac/rudix,rudix-mac/rudix