postgresql: fix shell version of pg_config.sh

[sgn]

@xtraeme @pullmoll Please help to pull this.
Sorry, but I've another thing to do.
The old version (#20783) may work because echo doesn't accept -W -f -L -l by now

[Piraty]

why now make echo a function

echo() { printf '%s\n' "$@" ; }

[sgn]

why now make echo a function

echo() { printf '%s\n' "$@" ; }

That would work, too.
I'll change it that way.

[pullmoll]

LGTM