Add WITH_XMSS, move to prevent conflicts.

Add #ifdef WITH_XMSS to ssh-xmss.c, move it in the other files to after
includes.h so it's less likely to conflict and will pick up WITH_XMSS if
added to config.h.

ssh-xmss.c

@@ -16,6 +16,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 #include "includes.h"
+#ifdef WITH_XMSS
 
 #define SSHKEY_INTERNAL
 #include <sys/types.h>
@@ -188,3 +189,4 @@ ssh_xmss_verify(const struct sshkey *key,
 	free(ktype);
 	return r;
 }
+#endif /* WITH_XMSS */

sshkey-xmss.c

@@ -1,4 +1,3 @@
-#ifdef WITH_XMSS
 /* $OpenBSD: sshkey-xmss.c,v 1.1 2018/02/23 15:58:38 markus Exp $ */
 /*
  * Copyright (c) 2017 Markus Friedl.  All rights reserved.
@@ -25,6 +24,7 @@
  */
 
 #include "includes.h"
+#ifdef WITH_XMSS
 
 #include <sys/types.h>
 #include <sys/uio.h>

xmss_commons.c

@@ -1,4 +1,3 @@
-#ifdef WITH_XMSS
 /*
 xmss_commons.c 20160722
 Andreas Hülsing
@@ -7,6 +6,7 @@ Public domain.
 */
 
 #include "includes.h"
+#ifdef WITH_XMSS
 
 #include "xmss_commons.h"
 #include <stdlib.h>

xmss_fast.c

@@ -1,4 +1,3 @@
-#ifdef WITH_XMSS
 /*
 xmss_fast.c version 20160722
 Andreas Hülsing
@@ -7,6 +6,7 @@ Public domain.
 */
 
 #include "includes.h"
+#ifdef WITH_XMSS
 
 #include "xmss_fast.h"
 #include <stdlib.h>

xmss_hash.c

@@ -1,4 +1,3 @@
-#ifdef WITH_XMSS
 /*
 hash.c version 20160722
 Andreas Hülsing
@@ -7,6 +6,7 @@ Public domain.
 */
 
 #include "includes.h"
+#ifdef WITH_XMSS
 
 #include "xmss_hash_address.h"
 #include "xmss_commons.h"

xmss_hash_address.c

@@ -1,4 +1,3 @@
-#ifdef WITH_XMSS
 /*
 hash_address.c version 20160722
 Andreas Hülsing
@@ -6,6 +5,7 @@ Joost Rijneveld
 Public domain.
 */
 #include "includes.h"
+#ifdef WITH_XMSS
 
 #ifdef HAVE_STDINT_H
 #include <stdint.h>

xmss_wots.c

@@ -1,4 +1,3 @@
-#ifdef WITH_XMSS
 /*
 wots.c version 20160722
 Andreas Hülsing
@@ -7,6 +6,7 @@ Public domain.
 */
 
 #include "includes.h"
+#ifdef WITH_XMSS
 
 #include <stdlib.h>
 #ifdef HAVE_STDINT_H