[Bug other/102664] contrib/gcc-git-customization.sh uses echo -n, which isn't portable

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102664

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
git-descr.sh uses ${r:-no} which is a bash feature, but the shebang says
/bin/sh