that manual page also gives this suggestion:

Note this make command, executed in the build directory, will do much the same thing, without the configuration difference and without building everything twice: make CXXFLAGS='-g3 -O0 -fno-inline' all

In reply to @siraben:matrix.org
Does Nix support Canadian cross-compilation?

Anyone see anything wrong with this?

let
  nixpkgs = import (import ./nix/sources.nix).nixpkgs {};
  gcc = nixpkgs.gcc.override (o: { cc = nixpkgs.gcc.cc.overrideAttrs (o: {
      dontStrip = true;
      configureFlags = o.configureFlags ++ [ "--enable-libstdcxx-debug" "--enable-languages=c++" ];
      hardeningDisable = [ "all" ];
      });});
in
with nixpkgs; mkShell {
  buildInputs  = [
    git
    niv
    valgrind
    gcc
    gdb
    cmake
    ];
  LD_LIBRARY_PATH = "${gcc.cc}/lib/debug";
  hardeningDisable = [ "all" ]; # clear extraneous compiler flags, I want to add things manually myself.
  }

(I think) When I try to add keepTreeHook, I run into:

cycle detected in the references of '/nix/store/bxspqrcrbqw9sbj3ap9rdrk4fpi8150h-gcc-10.3.0-lib' from '/nix/store/xrizkssnx1m7c0z1fji9qxd7kfd333jr-gcc-10.3.0'
error: build of '/nix/store/ck1vxcqvqzn488njy9iwhy8b90jznyd7-gcc-10.3.0.drv', '/nix/store/r6ipjr4ivr1lc61c2yxsk7l6xj9mdygs-gcc-wrapper-10.3.0.drv' failed