dmd: Fix bootstrap dmd to build with sandboxing of nixUnstable

pkgs/development/compilers/dmd/2.067.1.nix

@@ -43,6 +43,7 @@ stdenv.mkDerivation rec {
   # Compile with PIC to prevent colliding modules with binutils 2.28.
   # https://issues.dlang.org/show_bug.cgi?id=17375
   usePIC = "-fPIC";
+  ROOT_HOME_DIR = "$(echo ~root)";
 
   postPatch = ''
       # Ugly hack so the dlopen call has a chance to succeed.
@@ -70,6 +71,10 @@ stdenv.mkDerivation rec {
   + stdenv.lib.optionalString stdenv.hostPlatform.isLinux ''
       substituteInPlace dmd/src/root/port.c \
         --replace "#include <bits/mathdef.h>" "#include <complex.h>"
+
+      # See https://github.com/NixOS/nixpkgs/issues/29443
+      substituteInPlace phobos/std/path.d \
+          --replace "\"/root" "\"${ROOT_HOME_DIR}"
   ''
 
   + stdenv.lib.optionalString stdenv.hostPlatform.isDarwin ''