[libglnx] Include sys/mman.h when checking for memfd_create

[Alexander Larsson <alexl src gnome org>]

commit 0c82203cd459a35cc3f471e3205355e9fb79160f
Author: Aurelien Jarno <aurel32 debian org>
Date:   Sat Feb 17 23:57:53 2018 +0100

    Include sys/mman.h when checking for memfd_create
    
    glibc 2.27 added support for memfd_create. Unfortunately flatpak-builder,
    or rather the included libglnx library, also has such a function to
    wrap the corresponding syscall. It correctly tries to detect it in
    the configure script to disabled the wrapper in case glibc provides
    it. However it doesn't work due to a missing include.
    
    Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=890722

 libglnx.m4 |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/libglnx.m4 b/libglnx.m4
index d5bcc2f..34caf20 100644
--- a/libglnx.m4
+++ b/libglnx.m4
@@ -12,6 +12,7 @@ AC_CHECK_DECLS([
 #include <sched.h>
 #include <linux/loop.h>
 #include <linux/random.h>
+#include <sys/mman.h>
 ]])
 
 AC_ARG_ENABLE(otmpfile,