build: fix a warning on non-GNU distributions

Found on FreeBSD where /bin/sh descends from Almquist shell. It's very fast superset of POSIX (e.g., local keyword, $'...' quoting).

[[ is supported by Bash, Zsh, oksh but not by FreeBSD sh, NetBSD sh, dash, mrsh.

dash$ [[ foo = bar ]]
dash: 1: [[: not found

mrsh$ [[ foo = bar ]]
mrsh:0:0: syntax error: keyword is reserved and causes unspecified results: [[

See also https://gitlab.gnome.org/bilelmoussaoui/gtk-rust-template/-/merge_requests/52

The script specifically uses a #!/bin/bash shebang, why is it run via sh?

Oops, I was using 0.3.1 tag, so didn't notice 7b1b5ea3. -o pipefail is still compatible with /bin/sh at least on FreeBSD (ash), NetBSD (ash), OpenBSD (ksh) and busybox (dash fork).

Unfortunately, set -o pipefail is not posix sh and I'm not sure about set -e and set -u.

I don't want to be responsible for running rm -rf $HOME/$SOME_UNSET_VAR or similar when the script is changed somehow so I'm staying with bash, which hopefully isn't a problem, let me know otherwise.

closed