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

[redi at gcc dot gnu.org]

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

--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Ah, but 'expr match str re' is not in POSIX, it should be 'expr str : re'