[libglnx] missing-syscall: #include config.h

[Colin Walters <walters src gnome org>]

commit b36606b366d39c7ddb90ee21d622c0cb1da118ed
Author: Colin Walters <walters verbum org>
Date:   Thu Nov 2 11:30:53 2017 -0400

    missing-syscall: #include config.h
    
    Followup to previous commit; this helps me build libostree
    with `-Werror=undef`.

 glnx-missing-syscall.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/glnx-missing-syscall.h b/glnx-missing-syscall.h
index fef6e60..ebfd7f4 100644
--- a/glnx-missing-syscall.h
+++ b/glnx-missing-syscall.h
@@ -30,6 +30,7 @@
    Add abstraction model for BPF programs
 */
 
+#include "config.h"
 
 #if !HAVE_DECL_RENAMEAT2
 #  ifndef __NR_renameat2