Supply missing header guards

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190604181618.19980-5-armbru@redhat.com>
diff --git a/linux-user/cris/syscall_nr.h b/linux-user/cris/syscall_nr.h
index 44f0b64..4b6cf65 100644
--- a/linux-user/cris/syscall_nr.h
+++ b/linux-user/cris/syscall_nr.h
@@ -2,6 +2,9 @@
  * This file contains the system call numbers, and stub macros for libc.
  */
 
+#ifndef LINUX_USER_CRIS_SYSCALL_NR_H
+#define LINUX_USER_CRIS_SYSCALL_NR_H
+
 #define TARGET_NR_restart_syscall      0
 #define TARGET_NR_exit		  1
 #define TARGET_NR_fork		  2
@@ -360,3 +363,5 @@
 #define TARGET_NR_memfd_create       357
 #define TARGET_NR_bpf                358
 #define TARGET_NR_execveat           359
+
+#endif