https://src.fedoraproject.org/rpms/kakasi/raw/4756771349822d4ccd4d74a6ce70040ca57084cb/f/kakasi-configure-c99.patch
https://bugs.gentoo.org/874654

Avoid an implicit declaration of exit and build failures with future
compilers which do not support implicit function declarations by
default.

--- a/configure.in
+++ b/configure.in
@@ -85,7 +85,7 @@ AS_VAR_IF(utf8, "yes",[
     LIBS="$LIBICONV $LIBS"
     AC_DEFINE(KAKASI_SUPPORT_UTF8, 1, [KAKASI_SUPPORT_UTF8])
     AC_RUN_IFELSE([AC_LANG_PROGRAM([#include <iconv.h>],
-		    [if (iconv_open("EUC-JP", "UTF-8") == -1) exit(1);])],
+		    [if (iconv_open("EUC-JP", "UTF-8") == -1) return 1;])],
 	[],
 	[AC_MSG_ERROR([can not use EUC-JP or UTF-8 encoding on iconv])])
 ])