add linux-to-windows cross compile to msys_build.sh

be more careful about ARCH vs XC_HOST

use windows version of 7z with wine for cross-compile

use pcre_h.jl from binary instead of downloading pcre rpm

use a switch case, remove appveyor specific code
attempt cross compile on travis

set XC_HOST in env matrix

install p7zip-full

run the msys_build.sh script instead of make