Second attempt at fixing check-man

I was wrong, actually LANG-vs-LC_ALL only fixed one case, by mistake. To
get proper UTF-8 encoding, we need to enforce any UTF-8 locale. We
choose the 'default' of en_US.UTF-8.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

autotools/check-man

@@ -20,7 +20,7 @@
 
 set -e
 
-! LANG=C MANWIDTH=80 \
+! LANG=en_US.UTF-8 MANWIDTH=80 \
   man --warnings --encoding=utf8 --local-file "$1" 2>&1 >/dev/null | \
   grep -v -e "cannot adjust line" -e "can't break line" | \
   grep .