Use standard missing-syscalls with EXTRA_CFLAGS instead of duplicating
the command.  And move the archprepare rule before the archclean rule.
Suggested by Franck Bui-Huu.  Also add "echo" to show the target ABI.
Signed-off-by: NAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>