andy@xps:~/tmp$ NIX_DEBUG=true gcc
(some good flags for dealing with /nix/store/* and then...)
  -O2
  -D_FORTIFY_SOURCE=2
  -fstack-protector-strong
  --param
  ssp-buffer-size=4
  -fPIC
  -fno-strict-overflow
  -Wformat
  -Wformat-security
  -Werror=format-security

These flags should be enabled when compiling nix packages, but they should not be always on for general compiler use.

This has caused a broken debugging experience for me on the project I was working on.

Most projects have a "debug build" that has optimizations off, and this prevents that from working correctly.

NixOS version 16.09pre90254.6b20d5b (Flounder)