qemu_2.11.1.bb: support mingw build

qemu_2.11.1.bb: support mingw build

The patch chardev-connect-socket-to-a-spawned-command.patch calls
"socketpair". This function is missing in mingw, so the patch
needs to be modified accordingly (by conditional compilation using
_WIN32 macro where appropriate), otherwise we end up with a broken
mingw build.

While it is possible to simply remove the whole patch for mingw build
(via a .bbappend file in meta-mingw), it makes more sense to modify
the patch itself.

Signed-off-by: Juro Bystricky <juro.bystricky@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>