configure.ac: move AC_OUTPUT -> AC_CONFIG_FILES

Instead of having one file in AC_OUTPUT, and all others in
AC_CONFIG_FILES, move all of them to AC_CONFIG_FILES. Sort the files
while at it and have one per line.

Fix this warning:
  configure.ac:86: warning: AC_OUTPUT should be used without arguments.

Change-Id: Iea782b03c9ede154eedbd0c0e9f0d7359bb49967
diff --git a/configure.ac b/configure.ac
index a16f40b..2665b70 100644
--- a/configure.ac
+++ b/configure.ac
@@ -74,6 +74,14 @@
 
 AC_SUBST([CPPFLAGS])
 AC_SUBST([CFLAGS])
-AC_CONFIG_FILES([Makefile src/Makefile include/Makefile include/libgtpnl/Makefile include/linux/Makefile tools/Makefile libgtpnl.pc])
-AC_OUTPUT(
-	contrib/libgtpnl.spec)
+AC_CONFIG_FILES([
+	Makefile
+	contrib/libgtpnl.spec
+	include/Makefile
+	include/libgtpnl/Makefile
+	include/linux/Makefile
+	libgtpnl.pc
+	src/Makefile
+	tools/Makefile
+])
+AC_OUTPUT()