https://bugs.gentoo.org/955783
https://github.com/lttng/lttng-tools/pull/170

From 7d669a90212e105b0f669aa2ab38c987b187baab Mon Sep 17 00:00:00 2001
From: Hongxu Jia <hongxu.jia@windriver.com>
Date: Wed, 21 May 2025 13:09:25 +0800
Subject: [PATCH] fix lttng-tools fails to compile with libxml2 2.14.0+

Description:
| In file included from /srv/pokybuild/yocto-worker/qemux86-alt/build/build/tmp/work/core2-32-poky-linux/lttng-tools/2.13.15/recipe-sysroot/usr/include/libxml2/libxml/parser.h:25,
|                  from ../../../../lttng-tools-2.13.15/src/common/config/session-config.c:29:
| /srv/pokybuild/yocto-worker/qemux86-alt/build/build/tmp/work/core2-32-poky-linux/lttng-tools/2.13.15/recipe-sysroot/usr/include/libxml2/libxml/encoding.h:173:7: note: declared here
|   173 |     } input XML_DEPRECATED_MEMBER;
|       |       ^~~~~
| ../../../../lttng-tools-2.13.15/src/common/config/session-config.c:432:15: error: called object is not a function or function pointer
|   432 |         ret = handler->input(out_str, &out_len, (const xmlChar *) in_str, &in_len);
|       |               ^~~~~~~
| At top level:
| cc1: note: unrecognized command-line option '-Wno-incomplete-setjmp-declaration' may have been intended to silence earlier diagnostics

According to [1][2], the UTF-8 handler is
```
static xmlCharEncError
UTF8ToUTF8(void *vctxt ATTRIBUTE_UNUSED,
           unsigned char* out, int *outlen,
           const unsigned char* in, int *inlen,
           int flush ATTRIBUTE_UNUSED)
```

Update input.func with setting ATTRIBUTE_UNUSED params with NULL and 0

[1] https://gitlab.gnome.org/GNOME/libxml2/-/commit/38f475072aefe032fff1dc058df3e56c1e7062fa
[2] https://gitlab.gnome.org/GNOME/libxml2/-/commit/69b83bb68e2a8ed0013f80c51b9a358714b00c9a#478024cc18a2cc8dbaed34076e9775f6827f413d_2188_2201

Signed-off-by: Marko, Peter <Peter.Marko@siemens.com>
Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
--- a/src/common/config/session-config.c
+++ b/src/common/config/session-config.c
@@ -429,7 +429,7 @@ static xmlChar *encode_string(const char *in_str)
 		goto end;
 	}
 
-	ret = handler->input(out_str, &out_len, (const xmlChar *) in_str, &in_len);
+	ret = handler->input.func(NULL, out_str, &out_len, (const xmlChar *) in_str, &in_len, 0);
 	if (ret < 0) {
 		xmlFree(out_str);
 		out_str = NULL;