rustc --crate-type flag should display valid values

[disconnect3d]

Hello,

When we provide wrong value for the --emit flag, we will get a list of valid values. This is not the case for --crate-type flag, which should also display valid values.

The --emit example:

$ cargo rustc -- --emit=asd
   Compiling tokio v0.2.13 (/host/tokio/tokio)
error: unknown emission type: `asd` - expected one of: `llvm-bc`, `asm`, `llvm-ir`, `mir`, `obj`, `metadata`, `link`, `dep-info`

The --crate-type example:

$ cargo rustc -- --crate-type=dynlib
   Compiling tokio v0.2.13 (/host/tokio/tokio)
error: unknown crate type: `dynlib`

error: could not compile `tokio`.

To learn more, run the command again with --verbose.

Versions:

$ cargo --version
cargo 1.41.0 (626f0f40e 2019-12-03)
r$ rustc --version
rustc 1.41.0 (5e1a79984 2020-01-27)

I have also tested this on rustc 1.42.0 and it is the same.

[fmease]

rust/compiler/rustc_session/src/config.rs

Lines 2672 to 2681 in a7fc76a

	let new_part = match part {
	"lib" => default_lib_output(),
	"rlib" => CrateType::Rlib,
	"staticlib" => CrateType::Staticlib,
	"dylib" => CrateType::Dylib,
	"cdylib" => CrateType::Cdylib,
	"bin" => CrateType::Executable,
	"proc-macro" => CrateType::ProcMacro,
	_ => return Err(format!("unknown crate type: `{part}`")),
	};