Avoid including sys/prctl.h on the Hurd.

Upstream status: Not submitted.

--- shadow-4.8.1/libmisc/idmapping.c.orig	2020-03-07 16:32:05.000000000 -0500
+++ shadow-4.8.1/libmisc/idmapping.c	2020-03-07 16:32:27.000000000 -0500
@@ -36,8 +36,8 @@
 #include <stdio.h>
 #include "prototypes.h"
 #include "idmapping.h"
-#include <sys/prctl.h>
 #if HAVE_SYS_CAPABILITY_H
+#include <sys/prctl.h>
 #include <sys/capability.h>
 #endif
 
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<tr><td><span title='2020-07-20 23:25:09 +0200'>2020-07-20</span></td><td><a href='/guix/commit/m4?id=e8088f0b06c2193f2cce04a48aa1350229442a9f'>ssh: Speed up RPCs by using #:nodelay.</a><span class='msg-avail'>...</span></td><td>Lars-Dominik Braun</td></tr>
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