don't use libicu backend for libxml2

(it's discouraged from being used, the first path always goes through iconv, icu is only the fallback)

config/lib.json

@@ -450,6 +450,7 @@
     },
     "libmemcached": {
         "source": "libmemcached",
+        "cpp-library": true,
         "static-libs-unix": [
             "libmemcached.a",
             "libmemcachedprotocol.a",
@@ -594,7 +595,6 @@
         ],
         "lib-suggests-unix": [
             "xz",
-            "icu",
             "zlib"
         ],
         "lib-depends-windows": [

src/SPC/builder/unix/library/libxml2.php

@@ -20,10 +20,10 @@ trait libxml2
                 "-DZLIB_INCLUDE_DIR={$this->getIncludeDir()}",
                 '-DLIBXML2_WITH_ZLIB=OFF',
             )
-            ->optionalLib('icu', ...cmake_boolean_args('LIBXML2_WITH_ICU'))
             ->optionalLib('xz', ...cmake_boolean_args('LIBXML2_WITH_LZMA'))
             ->addConfigureArgs(
                 '-DLIBXML2_WITH_ICONV=ON',
+                '-DLIBXML2_WITH_ICU=OFF', // optional, but discouraged: https://gitlab.gnome.org/GNOME/libxml2/-/blob/master/README.md
                 '-DLIBXML2_WITH_PYTHON=OFF',
                 '-DLIBXML2_WITH_PROGRAMS=OFF',
                 '-DLIBXML2_WITH_TESTS=OFF',