dev-libs/libxml2: Sync with Gentoo

It's from Gentoo commit bee4fbd32b0225d09bf7fca8d38b83a9ac368bfd.

sdk_container/src/third_party/portage-stable/dev-libs/libxml2/files/libxml2-2.10.3-python3-unicode-errors.patch

@@ -0,0 +1,35 @@
+https://bugs.gentoo.org/745162
+https://gitlab.gnome.org/GNOME/libxml2/-/issues/64
+
+--- a/python/libxml.c
++++ b/python/libxml.c
+@@ -1620,6 +1620,7 @@ libxml_xmlErrorFuncHandler(ATTRIBUTE_UNU
+     PyObject *message;
+     PyObject *result;
+     char str[1000];
++    unsigned char *ptr = (unsigned char *)str;
+ 
+ #ifdef DEBUG_ERROR
+     printf("libxml_xmlErrorFuncHandler(%p, %s, ...) called\n", ctx, msg);
+@@ -1636,12 +1637,20 @@ libxml_xmlErrorFuncHandler(ATTRIBUTE_UNU
+ 	    str[999] = 0;
+         va_end(ap);
+ 
++#if PY_MAJOR_VERSION >= 3
++        /* Ensure the error string doesn't start at UTF8 continuation. */
++        while (*ptr && (*ptr & 0xc0) == 0x80)
++            ptr++;
++#endif
++
+         list = PyTuple_New(2);
+         PyTuple_SetItem(list, 0, libxml_xmlPythonErrorFuncCtxt);
+         Py_XINCREF(libxml_xmlPythonErrorFuncCtxt);
+-        message = libxml_charPtrConstWrap(str);
++        message = libxml_charPtrConstWrap(ptr);
+         PyTuple_SetItem(list, 1, message);
+         result = PyEval_CallObject(libxml_xmlPythonErrorFuncHandler, list);
++        /* Forget any errors caused in the error handler. */
++        PyErr_Clear();
+         Py_XDECREF(list);
+         Py_XDECREF(result);
+     }

sdk_container/src/third_party/portage-stable/dev-libs/libxml2/libxml2-2.10.3-r1.ebuild

@@ -56,6 +56,8 @@ MULTILIB_CHOST_TOOLS=(
 	/usr/bin/xml2-config
 )
 
+PATCHES=( "${FILESDIR}"/${PN}-2.10.3-python3-unicode-errors.patch )
+
 DOCS=( NEWS README.md TODO TODO_SCHEMAS python/TODO )
 
 src_unpack() {