Swith to gtk+2.
From Debian's corewars_0.9.13+ds-1.diff.

--- configure.ac.orig	Wed Oct 23 14:49:46 2002
+++ configure.ac	Wed Mar 24 23:16:44 2010
@@ -36,38 +36,29 @@ AM_PROG_LEX
 AC_PROG_LN_S
 
 COREWARS=corewars
-AM_PATH_GLIB(1.2.0,,COREWARS=;AC_MSG_ERROR([
+AM_PATH_GLIB_2_0(2.0.0,,COREWARS=;AC_MSG_ERROR([
 
    ************************************************************************
-   *** GLIB >= 1.2.0 not installed - cannot build GUI client without it ***
+   *** GLIB >= 2.0.0 not installed - cannot build GUI client without it ***
    ************************************************************************
 ]))
-AM_PATH_GTK(1.2.0,,COREWARS=;AC_MSG_ERROR([
+AM_PATH_GTK_2_0(2.0.0,,COREWARS=;AC_MSG_ERROR([
 
    ************************************************************************
-   *** GTK+ >= 1.2.0 not installed - cannot build GUI client without it ***
+   *** GTK+ >= 2.0.0 not installed - cannot build GUI client without it ***
    ************************************************************************
 ]))
 
 LIBS="$LIBS $GTK_LIBS"
-GTK_INCLUDE=`gtk-config --cflags`
 AC_SUBST(INCLUDES)
-INCLUDES="$INCLUDES $GTK_INCLUDE"
+INCLUDES="$INCLUDES $GTK_CFLAGS"
 
 dnl Checks for header files.
 AC_HEADER_DIRENT
 AC_STDC_HEADERS
 AC_CHECK_HEADERS(limits.h malloc.h string.h unistd.h)
 
-dnl Check for libc >= 2.1
-COREWARSCMD=
-AC_CHECK_HEADERS(argp.h,COREWARSCMD=corewars-cmd,AC_MSG_WARN([
-
-   ********************************************************************************
-   *** glibc >= 2.1 not installed - cannot build command line client without it ***
-   ***                        (but this is ok if you want the GTK+ client only) ***
-   ********************************************************************************
-]))
+COREWARSCMD=corewars-cmd
 
 dnl Checks for typedefs, structures, and compiler characteristics.
 AC_C_CONST
