[mutter] build: Fix KMS backend summary printout

[Bastien Nocera <hadess src gnome org>]

commit 97d180ee598139f464949e58a2d33f87f5e88b97
Author: Bastien Nocera <hadess hadess net>
Date:   Fri Jul 29 16:22:58 2016 +0200

    build: Fix KMS backend summary printout
    
    If have_native_backend is not set, we might end up with:
        Native (KMS) backend:
    instead of:
        Native (KMS) backend:     no
    
    in the configure summary
    
    https://bugzilla.gnome.org/show_bug.cgi?id=769305

 configure.ac |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index ae18984..2756145 100644
--- a/configure.ac
+++ b/configure.ac
@@ -243,6 +243,7 @@ AC_ARG_ENABLE(native-backend,
   AS_HELP_STRING([--disable-native-backend], [disable mutter native (KMS) backend]),,
   enable_native_backend=auto
 )
+have_native_backend="no"
 AS_IF([test "$enable_native_backend" = "yes"], [have_native_backend=yes],
       [test "$enable_native_backend" = "auto"], PKG_CHECK_EXISTS([$MUTTER_NATIVE_BACKEND_MODULES], 
[have_native_backend=yes]))