package/libxml2: fix compilation with GCC 14.x and uClibc

The patch fixes the following errors and warnings raised by the
compilation of libxml2 with the combination of GCC 14.x and uClibc.

encoding.c: In function ‘xmlEncInputChunk’:
encoding.c:2209:32: warning: comparison between pointer and integer
 2209 |     else if (handler->iconv_in != NULL) {
      |                                ^~
encoding.c: In function ‘xmlEncOutputChunk’:
encoding.c:2269:33: warning: comparison between pointer and integer
 2269 |     else if (handler->iconv_out != NULL) {
      |                                 ^~
encoding.c: In function ‘xmlCharEncCloseFunc’:
encoding.c:2681:29: warning: comparison between pointer and integer
 2681 |     if ((handler->iconv_out != NULL) || (handler->iconv_in != NULL)) {
      |                             ^~
encoding.c:2681:60: warning: comparison between pointer and integer
 2681 |     if ((handler->iconv_out != NULL) || (handler->iconv_in != NULL)) {
      |                                                            ^~
encoding.c:2683:32: warning: comparison between pointer and integer
 2683 |         if (handler->iconv_out != NULL) {
      |                                ^~
encoding.c:2686:32: error: assignment to ‘iconv_t’ {aka ‘long int’} from ‘void *’ makes integer from pointer without a cast [-Wint-conversion]
 2686 |             handler->iconv_out = NULL;
      |                                ^
encoding.c:2688:31: warning: comparison between pointer and integer
 2688 |         if (handler->iconv_in != NULL) {
      |                               ^~
encoding.c:2691:31: error: assignment to ‘iconv_t’ {aka ‘long int’} from ‘void *’ makes integer from pointer without a cast [-Wint-conversion]
 2691 |             handler->iconv_in = NULL;
      |                               ^
make[4]: *** [Makefile:1147: libxml2_la-encoding.lo] Error 1

This code has been in libxml2 pretty much forever: it was partially
introduced in version 2.1.0: 496a1cf59284 ("496a1cf59284 revamped the
encoding support, added iconv support, so now libxml if") and
partially in version 2.2.3: 87b953957305 ("Large sync between my W3C
base and Gnome's one:"). And the first time Buildroot packaged
libxml2, it was version 2.6.29.

However, both glibc and musl define iconv_t as "void *", which meant
the libxml2 code was not problematic. uClibc defines iconv_t as
"long", which generated only a warning... until GCC got updated to GCC
14.x, which turned this warning into an error, causing the build
failure.

Fixes:

  http://autobuild.buildroot.net/results/fd4f8d2e8d8ee68d9e18f761ceff350188e55a87/

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit ca63c4409b3c811e8c4ee19c2860c53af35c4ce1)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libxml2/0001-Fix-compilation-with-uclibc.patch

@@ -0,0 +1,114 @@
+From fc72e0833a4e5724aef604e2fd9adb1014cb4844 Mon Sep 17 00:00:00 2001
+From: Dario Binacchi <dario.binacchi@amarulasolutions.com>
+Date: Mon, 16 Dec 2024 17:23:23 +0100
+Subject: [PATCH] Fix compilation with uclibc
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+The patch fixes the following errors and warnings raised by the
+compilation of the library with uClibc:
+
+encoding.c: In function ‘xmlEncInputChunk’:
+encoding.c:2209:32: warning: comparison between pointer and integer
+ 2209 |     else if (handler->iconv_in != NULL) {
+      |                                ^~
+encoding.c: In function ‘xmlEncOutputChunk’:
+encoding.c:2269:33: warning: comparison between pointer and integer
+ 2269 |     else if (handler->iconv_out != NULL) {
+      |                                 ^~
+encoding.c: In function ‘xmlCharEncCloseFunc’:
+encoding.c:2681:29: warning: comparison between pointer and integer
+ 2681 |     if ((handler->iconv_out != NULL) || (handler->iconv_in != NULL)) {
+      |                             ^~
+encoding.c:2681:60: warning: comparison between pointer and integer
+ 2681 |     if ((handler->iconv_out != NULL) || (handler->iconv_in != NULL)) {
+      |                                                            ^~
+encoding.c:2683:32: warning: comparison between pointer and integer
+ 2683 |         if (handler->iconv_out != NULL) {
+      |                                ^~
+encoding.c:2686:32: error: assignment to ‘iconv_t’ {aka ‘long int’} from ‘void *’ makes integer from pointer without a cast [-Wint-conversion]
+ 2686 |             handler->iconv_out = NULL;
+      |                                ^
+encoding.c:2688:31: warning: comparison between pointer and integer
+ 2688 |         if (handler->iconv_in != NULL) {
+      |                               ^~
+encoding.c:2691:31: error: assignment to ‘iconv_t’ {aka ‘long int’} from ‘void *’ makes integer from pointer without a cast [-Wint-conversion]
+ 2691 |             handler->iconv_in = NULL;
+      |                               ^
+make[4]: *** [Makefile:1147: libxml2_la-encoding.lo] Error 1
+
+Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
+Upstream: https://gitlab.gnome.org/GNOME/libxml2/-/commit/fc72e0833a4e5724aef604e2fd9adb1014cb4844
+---
+ encoding.c | 20 ++++++++++----------
+ 1 file changed, 10 insertions(+), 10 deletions(-)
+
+diff --git a/encoding.c b/encoding.c
+index 14ffafddbc02..41ecde1885e4 100644
+--- a/encoding.c
++++ b/encoding.c
+@@ -1264,7 +1264,7 @@ DECLARE_ISO_FUNCS(16)
+ #endif /* LIBXML_ISO8859X_ENABLED */
+ 
+ #ifdef LIBXML_ICONV_ENABLED
+-  #define EMPTY_ICONV , (iconv_t) 0, (iconv_t) 0
++  #define EMPTY_ICONV , (iconv_t) -1, (iconv_t) -1
+ #else
+   #define EMPTY_ICONV
+ #endif
+@@ -1389,8 +1389,8 @@ xmlNewCharEncodingHandler(const char *name,
+     handler->name = up;
+ 
+ #ifdef LIBXML_ICONV_ENABLED
+-    handler->iconv_in = NULL;
+-    handler->iconv_out = NULL;
++    handler->iconv_in = (iconv_t) -1;
++    handler->iconv_out = (iconv_t) -1;
+ #endif
+ #ifdef LIBXML_ICU_ENABLED
+     handler->uconv_in = NULL;
+@@ -2200,7 +2200,7 @@ xmlEncInputChunk(xmlCharEncodingHandler *handler, unsigned char *out,
+         }
+     }
+ #ifdef LIBXML_ICONV_ENABLED
+-    else if (handler->iconv_in != NULL) {
++    else if (handler->iconv_in != (iconv_t) -1) {
+         ret = xmlIconvWrapper(handler->iconv_in, out, outlen, in, inlen);
+     }
+ #endif /* LIBXML_ICONV_ENABLED */
+@@ -2260,7 +2260,7 @@ xmlEncOutputChunk(xmlCharEncodingHandler *handler, unsigned char *out,
+         }
+     }
+ #ifdef LIBXML_ICONV_ENABLED
+-    else if (handler->iconv_out != NULL) {
++    else if (handler->iconv_out != (iconv_t) -1) {
+         ret = xmlIconvWrapper(handler->iconv_out, out, outlen, in, inlen);
+     }
+ #endif /* LIBXML_ICONV_ENABLED */
+@@ -2672,17 +2672,17 @@ xmlCharEncCloseFunc(xmlCharEncodingHandler *handler) {
+      * Iconv handlers can be used only once, free the whole block.
+      * and the associated icon resources.
+      */
+-    if ((handler->iconv_out != NULL) || (handler->iconv_in != NULL)) {
++    if ((handler->iconv_out != (iconv_t) -1) || (handler->iconv_in != (iconv_t) -1)) {
+         tofree = 1;
+-	if (handler->iconv_out != NULL) {
++	if (handler->iconv_out != (iconv_t) -1) {
+ 	    if (iconv_close(handler->iconv_out))
+ 		ret = -1;
+-	    handler->iconv_out = NULL;
++	    handler->iconv_out = (iconv_t) -1;
+ 	}
+-	if (handler->iconv_in != NULL) {
++	if (handler->iconv_in != (iconv_t) -1) {
+ 	    if (iconv_close(handler->iconv_in))
+ 		ret = -1;
+-	    handler->iconv_in = NULL;
++	    handler->iconv_in = (iconv_t) -1;
+ 	}
+     }
+ #endif /* LIBXML_ICONV_ENABLED */
+-- 
+2.43.0
+