build: fix some mingw issues

build: fix some mingw issues

On Fedora 13 with sufficient mingw32-* packages installed, running
./autobuild.sh failed to cross-compile to mingw because
mingw32-pthreads installed a broken <pthread.h>.  With that
issue fixed, the build still failed due to use of O_SYNC.
Meanwhile, recent .spec.in changes got out of sync.

* bootstrap.conf (gnulib_modules): Add fcntl-h, for O_SYNC.
* .gnulib: Update to latest, to work around buggy pthreads-win32
library.
* bootstrap: Import latest from gnulib.
* mingw32-libvirt.spec.in: Distribute new file.