[PATCH][libxshmfence] configure.ac: call AC_USE_SYSTEM_EXTENSIONS

[Ross Burton]

With glibc 2.27 memfd_create() is inside a _GNU_SOURCE guard, so call
AC_USE_SYSTEM_EXTENSIONS to get this defined.

Signed-off-by: Ross Burton <ross.burton at intel.com>
---
 configure.ac | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/configure.ac b/configure.ac
index 0c98875..ebf4dee 100644
--- a/configure.ac
+++ b/configure.ac
@@ -28,6 +28,8 @@ AC_INIT([libxshmfence], [1.2],
 AC_CONFIG_SRCDIR([Makefile.am])
 AC_CONFIG_HEADERS([config.h])
 
+AC_USE_SYSTEM_EXTENSIONS
+
 # Initialize Automake
 AM_INIT_AUTOMAKE([foreign dist-bzip2])
 
-- 
2.11.0