error: environment variable `\t` not defined at compile time
  --> $DIR/extenv-escaped-var.rs:2:5
   |
LL |     env!("\t");
   |     ^^^^^^^^^^
   |
   = help: use `std::env::var("\t")` to read the variable at run time
   = note: this error originates in the macro `env` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 1 previous error