git-version-gen: avoid test -z portability glitch Autoconf warns that there are some broken shells where 'test -z "$x"' gives 0 exit status if $x is ')'. Since some of our strings come from command-line arguments, and since git-version-gen is run on end-user machines where sh might be broken, we should be robust to abuse. Some of the instances replaced here are provably safe, and could not confuse even broken 'test', but it is easier to replace all instances of test -[nz]. * build-aux/git-version-gen: Prefer portable test spelling, since git-version-gen is run on more than just developer machines. Signed-off-by: Eric Blake <eblake@redhat.com>