Fix X11 and rust build on arm64

scripts.d/45-x11/50-libxext.sh

@@ -5,7 +5,6 @@ LIBXEXT_COMMIT="47904063048fa6ef6e8e16219ddef4d14d5d9a4b"
 
 ffbuild_enabled() {
     [[ $TARGET != linux* ]] && return -1
-    [[ $TARGET == linuxarm64 ]] && return -1
     return 0
 }
 
@@ -26,6 +25,12 @@ ffbuild_dockerbuild() {
         --without-lint
     )
 
+    if [[ $TARGET == linuxarm64 ]]; then
+        myconf+=(
+            --disable-malloc0returnsnull
+        )
+    fi
+
     if [[ $TARGET == linux* ]]; then
         myconf+=(
             --host="$FFBUILD_TOOLCHAIN"