makekeys: fix cross-compilation

makekeys: fix cross-compilation

makekeys must be built with the build-native compiler, not with $(CC)
which is the cross-compiler. The only sane way to achieve this seems to
be to use a separate Makefile.am for it.

This patch fixes the problem apparently caused by:

commit b5efe41f190cbb76eb1ca8ddf0c96990ddb83704
Author: Ran Benita <ran234@gmail.com>
Date:   Sat Mar 24 04:48:31 2012 +0200

    Make build non-recursive

There is no such thing as makekeys_makekeys_CC in automake.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>