Fix quoted const on Windows

Author: NattyNarwhal

ext/iconv/config.w32

@@ -11,7 +11,7 @@ if (PHP_ICONV != "no") {
 
 		AC_DEFINE("HAVE_ICONV", 1, "Define to 1 if the PHP extension 'iconv' is available.");
 		AC_DEFINE("HAVE_LIBICONV", 1, "Define to 1 if you have the 'libiconv' function.");
-		AC_DEFINE("ICONV_CONST", "", "Define to const if iconv's input is const.");
+		AC_DEFINE("ICONV_CONST", "", "Define to const if iconv's input is const.", false);
 		AC_DEFINE("ICONV_ALIASED_LIBICONV", 1, "Define to 1 if 'iconv()' is aliased to 'libiconv()'.");
 		AC_DEFINE("PHP_ICONV_IMPL", "\"libiconv\"", "The iconv implementation.");
 		ADD_FLAG("CFLAGS_ICONV", "/D PHP_ICONV_EXPORTS ");