virsh: fix build on mingw, which lacks termios stuff

virsh: fix build on mingw, which lacks termios stuff

Recent patches to fix handling of Ctrl-C when interacting with
ssh are not portable to mingw, which lacks termios handling.
The simplest solution is to just compile that code out, and
if someone ever appears that has a serious interest in getting
virsh fully functional even with ssh connections, they can
provide patches at that time.

* tools/virsh.h (_vshControl): Make termattr conditional.
* tools/virsh.c (vshTTYIsInterruptCharacter)
(vshTTYDisableInterrupt, vshTTYRestore, cfmakeraw, vshTTYMakeRaw)
(main): Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>