Stop defining VOID_SPRINTF, following what upstream libXpm does.  The
check has an implicit declaration of exit and an implicit int, so it
will fail to build with future compilers.

diff --git a/acinclude.m4 b/acinclude.m4
index 88edfce3d169a267..38409a28a65cb028 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -45,19 +45,6 @@ if test $lt_cv_xthreads = yes; then
 fi
 ])
 
-dnl This test is not very reliable probably ...
-AC_DEFUN([AM_FUNC_VOID_SPRINTF],
-[AC_CACHE_CHECK(whether sprintf returns void, ac_cv_func_void_sprintf,
-[AC_TRY_RUN([#include <stdio.h>
-int sprintf(); main() { exit(sprintf(".")); }],
-  ac_cv_func_void_sprintf=no, ac_cv_func_void_sprintf=yes, ac_cv_func_void_sprintf=yes)])
-if test $ac_cv_func_void_sprintf = no; then
-  AC_DEFINE(VOID_SPRINTF,1,
-  [Define if sprintf doesn't return the number of chars written])
-fi
-])
-
-
 dnl
 dnl End of special macros.
 dnl
diff --git a/configure.ac b/configure.ac
index 3b412361e6f43da4..6cbeb2f5eea235eb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -120,7 +120,6 @@ AC_FUNC_STRCOLL
 AC_FUNC_STRFTIME
 AC_FUNC_FORK([])
 AC_FUNC_VPRINTF
-AM_FUNC_VOID_SPRINTF
 AC_CHECK_FUNCS(wcslen wcscpy wcsncpy wcschr wcscat wcsncat getcwd gettimeofday mkdir re_comp regcmp select strcspn strerror strstr strtod strtol uname)
 AC_CHECK_FUNCS(strdup,,AC_DEFINE(NEED_STRDUP, 1, no strdup))
 AC_CHECK_FUNCS(strcasecmp,,AC_DEFINE(NEED_STRCASECMP, 1, no strcasecmp))