Use system lld on NixOS instead of rust-lld (#30123)

The -Zgcc-ld=lld flag makes rust use the rust-lld
linker that is distributed as part of rust toolchain.
However, this flag doesn't work on nixos correctly
as
  1) rust-lld needs to be patched to have the correct rpath
     to find libz.so
  2) the bin/gcc-ld/ld.lld wrapper which calls rust-lld also
     needs to be patched to use the correct dynamic loader
  3) rust-lld doesn't respect NIX_LDFLAGS which contains
     the additional search path derived from buildInputs.
     The system linkers on nixos are wrapped so that
     NIX_LDFLAGS is added as the rpath to the final binary.

Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>

etc/shell.nix

@@ -17,6 +17,7 @@ clangStdenv.mkDerivation rec {
     gst_all_1.gst-plugins-bad
 
     rustup
+    llvmPackages.bintools # provides lld
 
     # Build utilities
     cmake dbus gcc git pkg-config which llvm autoconf213 perl yasm m4