xbps-src/shutils/cross.sh: error out if cross toolchain can't be compiled
xbps-src/shutils/cross.sh: error out if cross toolchain can't be compiled

$rval was the return code of pkg_available and not of build.sh, since
pkg_available returns 0. because of this install_cross_pkg() would
always return 0 for success.

necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages,necrophcodr/void-packages