Use AC_USE_SYSTEM_EXTENSIONS and include <config.h>, so that <wchar.h>
makes a declaration of wcwidth available.  Include <glib/gprintf.h>
for a declaration of g_vasprintf.  This avoids implicit function
declarations and build failures with future compilers.

No need to upstream this because it only impacts the bundled 0.6.8
sources, the later 0.8.0 version has already been fixed upstream.  The
g_vasprintf call was introduced in the paps-0.6.6-lcnumeric.patch
downstream patch.

diff -ur paps-0.8.0.orig/paps-0.6.8/configure.in paps-0.8.0/paps-0.6.8/configure.in
--- paps-0.8.0.orig/paps-0.6.8/configure.in	2023-04-13 11:56:29.571277839 +0200
+++ paps-0.8.0/paps-0.6.8/configure.in	2023-04-13 12:00:03.228135149 +0200
@@ -6,6 +6,7 @@
 AC_LANG_C
 AC_PROG_CC
 AM_PROG_LIBTOOL
+AC_USE_SYSTEM_EXTENSIONS
 
 dnl ======================================================
 dnl check for CUPS
diff -ur paps-0.8.0.orig/paps-0.6.8/src/paps.c paps-0.8.0/paps-0.6.8/src/paps.c
--- paps-0.8.0.orig/paps-0.6.8/src/paps.c	2023-04-13 11:56:29.583277719 +0200
+++ paps-0.8.0/paps-0.6.8/src/paps.c	2023-04-13 12:02:28.958673663 +0200
@@ -20,7 +20,7 @@
  *
  */
 
-
+#include <config.h>
 #include <pango/pango.h>
 #include <pango/pangoft2.h>
 #include "libpaps.h"
diff -ur paps-0.8.0.orig/paps-0.6.8/src/libpaps.c paps-0.8.0/paps-0.6.8/src/libpaps.c
--- paps-0.8.0.orig/paps-0.6.8/src/libpaps.c	2023-04-13 11:56:29.581277739 +0200
+++ paps-0.8.0/paps-0.6.8/src/libpaps.c	2023-04-13 12:07:17.504779917 +0200
@@ -23,6 +23,7 @@
 
 #include "libpaps.h"
 
+#include <glib/gprintf.h>
 #include <pango/pango.h>
 #include <pango/pangoft2.h>
 #include <ft2build.h>