setup: disable -mno-cygwin if building under mingw32
This gcc option has been deprecated since at least 2009 (gcc 4.4),
and it causes compilations to fail entirely with gcc 4.6.x.
Upstream distutils bug: http://bugs.python.org/issue12641
$ "$TESTDIR/hghave" inotify || exit 80
$ hg init
$ echo "[extensions]" > .hg/hgrc
$ echo "inotify=" >> .hg/hgrc
$ hg inserve -d --pid-file .hg/inotify.pid
$ echo a > a
$ hg ci -Aqm0
$ hg co -q null
$ hg co -q
$ hg st
$ cat a
a
$ kill `cat .hg/inotify.pid`