Log Message:
print/a2ps: Fix mempcpy for DragonFly

a2ps is inconsistent with it's use of mempcpy.  For lib/path-concat.c and
lib/strftime.c, it's looking for "mempcpy", but for src/regex.c it is
looking for __mempcpy.

DragonFly has mempcpy in string.h, so just patch the problematic
lib/path-concat.c to stop it from being redefined.  HAVE_MEMPCPY isn't
defined correctly and if it were it would break at regex.c.  The string.h
header and mempcpy definition are mutually exclusive in strftime.c file
so this one didn't need a patch.