When `std` is missing the error message is very poor

[Lokathor]

A newbie Rustacean was trying to use the gba crate and they forgot to put #![no_std] in the lib.rs of their downstream project. The GBA uses a Tier 3 target with build-std, and so they landed on this error:

error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv4t-none-eabi` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: could not compile `gba-rust`

This is a poor experience. It's pretty vague about what went wrong, and has no suggestion of what the person can do to try and fix it.

Ideally, the error message should say something like:

std is required by cratenamehere because it does not declare #![no_std]

And then the user can have at least an idea of what to investigate.

[jonas-schievink]

related: #32663