Check for unshare on the configure and provide an inline replacement when not available

configure.ac

@@ -187,6 +187,16 @@ fi
 AC_SUBST(ACL_LIBS)
 AM_CONDITIONAL([HAVE_ACL], [test "x$have_acl" != xno])
 
+# ------------------------------------------------------------------------------
+
+AC_CHECK_DECL([unshare],
+        [AC_DEFINE(HAVE_UNSHARE, 1, [Define if unshare is declared])],
+        [AC_CHECK_DECL([SYS_unshare],
+                [ ] ,
+                [AC_MSG_ERROR([*** unshare nor SYS_unshare found.])],
+                [#include <syscall.h>])],
+        [#include <sched.h>])
+
 # ------------------------------------------------------------------------------
 AC_ARG_WITH(firmware-path,
        AS_HELP_STRING([--with-firmware-path=DIR[[[:DIR[...]]]]],

src/test/test-udev.c

@@ -31,16 +31,13 @@
 #include <sched.h>
 #include <sys/mount.h>
 #include <sys/signalfd.h>
-#include <sys/syscall.h>
 
 #include "udev.h"
 
-#ifndef SYS_unshare
-#error "libc fails to set SYS_unshare: please file a bug report with eudev"
-#endif
-
-#ifndef unshare
-#define unshare(__X) syscall(SYS_unshare, __X)
+#ifndef HAVE_UNSHARE
+#include <sys/syscall.h>
+/* Provide our own replacement with local reach*/
+static inline int unshare (int x) { return syscall(SYS_unshare, x); }
 #endif
 
 void udev_main_log(struct udev *udev, int priority,