Of the form:

../xkb/XKBGAlloc.c: In function ‘SrvXkbAddGeomKeyAlias’:
../xkb/XKBGAlloc.c:591:13: warning: ‘strncpy’ specified bound 4 equals destination size [-Wstringop-truncation]
             strncpy(alias->real, realStr, XkbKeyNameLength);
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is intentional; the code that reads from these fields never reads
more than 4 bytes anyway. Rephrase things in terms of memcpy so that's
clear. Obviously this is awful but in XKB awful is par.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Acked-by: Keith Packard <keithp@keithp.com>