[Qemu-devel] don't look for libuuid on Darwin

[C.W. Betts]

In Darwin, the libSystem.B.dylib is a container for a lot of  
libraries, among them is libuuid.  However, there isn't, by default, a  
static link  libuuid to libSystem.  The configure script should just  
check to see if there's a uuid header and don't look for a libuuid.