Use custom fd build with jemalloc tuned for Asahi

home/common.nix

@@ -1,5 +1,16 @@
 { config, pkgs, lib, ... }:
 
+let
+  fd =
+    if pkgs.stdenv.isAarch64 && pkgs.stdenv.isLinux then
+      pkgs.fd.overrideAttrs
+        (attrs:
+          {
+            preBuild = ''
+              export JEMALLOC_SYS_WITH_LG_PAGE=16
+            '';
+          }) else pkgs.fd;
+in
 {
   imports = [
     ./kakoune/kak.nix