build: fix globbing of extensions in other locales

In the fi_FI locale, [a-z] would not include 'w', for example. Rectify
this by using [[:alnum:]] (to counter against different ordering) and
forcing the POSIX locale (so that the alphabet has at least the 26
base characters).

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
1 file changed