Add build script for Cygwin from jenkins

[ChrisJefferson]

I put the current script used internally in St Andrews below, so others can see it:

tar jxf GAP-master-snapshot.tar.bz2
rm GAP-master-snapshot.tar.bz2
cd GAP-master-snapshot
./autogen.sh
./configure
make

# BUILDING PACKAGES

cd pkg
../bin/BuildPackages.sh
cat ./log/fail.log
# temporary removing binaries for ANUPQ and ACE
# see https://github.com/gap-system/gap/issues/1820
rm -rf anupq-*/bin
rm -rf ace-*/bin
# Delete unpackage carat code from carat package,
# see https://github.com/gap-system/gap-distribution/issues/55
rm -rf carat/carat
cd ..

# END OF BUILDING PACKAGES

cd bin
sed -i 's/cygwin\\bin/Users\\jenkins\\workspace\\GAP-master-windows-build\\GAP-master-snapshot\\bin\\i686-pc-cygwin-default32-kv8/g' gap.bat
sed -i 's/cygwin\\bin/Users\\jenkins\\workspace\\GAP-master-windows-build\\GAP-master-snapshot\\bin\\i686-pc-cygwin-default32-kv8/g' gapcmd.bat
cd ..

bin/instcygwinterminfo.sh
bin/gap.sh -A tst/testinstall.g || true
cp /bin/cyggcc_s-1.dll /bin/cyggmp-10.dll /bin/cygncursesw-10.dll /bin/cygpanelw-10.dll /bin/cygpopt-0.dll /bin/cygreadline7.dll /bin/cygstart.exe /bin/cygstdc++-6.dll /bin/cygwin1.dll /bin/mintty.exe /usr/bin/cygz.dll /usr/bin/rxvt.exe /usr/bin/regtool.exe /usr/i686-w64-mingw32/sys-root/mingw/bin/zlib1.dll bin/i686-pc-cygwin-default32-kv8
cp /bin/cygcurl* /bin/cygidn* /bin/cygcrypto* /bin/cyggssapi* /bin/cyglber* /bin/cygldap* /bin/cygssh* /bin/cygssl* /bin/cygkrb* /bin/cygk5crypto* /bin/cygintl* /bin/cygcom_err* /bin/cygunistring* /bin/cygiconv* /bin/cygsasl* bin/i686-pc-cygwin-default32-kv8
cd ..
zip -qq -r GAP-master-windows-build.zip GAP-master-snapshot/