error: macro-expanded `extern crate` items cannot shadow names passed with `--extern`
  --> $DIR/extern-prelude-extern-crate-fail.rs:16:9
   |
LL |         extern crate std as non_existent;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...
LL | define_std_as_non_existent!();
   | ----------------------------- in this macro invocation
   |
   = note: this error originates in the macro `define_std_as_non_existent` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0433]: failed to resolve: use of undeclared crate or module `two_macros`
  --> $DIR/extern-prelude-extern-crate-fail.rs:10:9
   |
LL |         two_macros::m!();
   |         ^^^^^^^^^^ use of undeclared crate or module `two_macros`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0433`.