Yes, but the devil is in the details. I'm trying to come up with some
sort of generic solution where you add a file
CYGWIN-PATCHES/upstream_patches.lst, whose contents (if the file exists)
is a list of patch files that should be bundled into the patch tarball,
and which should be applied before generating the cygwin-specific diff.
Then, based on the existance of CYGWIN-PATCHES/upstream_patchlist, g-b-s
would generate either a plain foo-1.1-1.patch (no upstream patches
provided), or a tarball foo-1.1-1.patch.tar.bz2 with both the upstream and
cygwin patches.