Ensure hyphen/minus is treated as literal in regexes

Ensure hyphen/minus is treated as literal in regexes

Each U+002D HYPHEN-MINUS in [0-9A-Za-z_-/.\] is treated as a member of a
range. The third one, which appears to have been intended to be a
literal, is part of an empty range because the starting point
U+005F LOW LINE is greater than the endpoint U+002F SOLIDUS, resulting
in at least some grep implementations not considering U+002D, U+002F
or U+005F to match the pattern. This resulted in one of the
dbus-launch tests being unintentionally skipped when it used a
regex based on the one in the spec.

regex(7) suggests "To include a literal '-' [in a bracketed character
set], make it the first or last character".

Signed-off-by: Simon McVittie <smcv@collabora.com>
Reviewed-by: Philip Withnall <withnall@endlessm.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=100686