improve ifdef check with decode_subcall

Use the same ifdef logic around the call sites of decode_subcall()
to protect the definition of the func itself.  This fixes warnings
for targets like hppa which don't use this func.

* syscall.c (decode_subcall): Wrap in SYS_socket_subcall and
SYS_ipc_subcall define checks.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
1 file changed