Merge CompilerError::CompilationFailed and CompilerError::ICE.

[nnethercote]

CompilerError has CompilationFailed and ICE variants, which seems reasonable at first. But the way it identifies them is flawed:

• If compilation errors out, i.e. RunCompiler::run returns an Err, it uses CompilationFailed, which is reasonable.
• If compilation panics with FatalError, it catches the panic and uses ICE. This is sometimes right, because ICEs do cause FatalError panics, but sometimes wrong, because certain compiler errors also cause FatalError panics. (The compiler/rustdoc/clippy/whatever just catches the FatalError with catch_with_exit_code in main.)

In other words, certain non-ICE compilation failures get miscategorized as ICEs. It's not possible to reliably distinguish the two cases, so this commit merges them. It also renames the combined variant as just Failed, to better match the existing Interrupted and Skipped variants.

Here is an example of a non-ICE failure that causes a FatalError panic, from tests/ui/recursion_limit/issue-105700.rs:

 #![recursion_limit="4"]
 #![invalid_attribute]
 #![invalid_attribute]
 #![invalid_attribute]
 #![invalid_attribute]
 #![invalid_attribute]
 //~^ERROR recursion limit reached while expanding

 fn main() {{}}

r? @spastorino

[rustbot]

This PR changes Stable MIR

cc @oli-obk, @celinval, @spastorino, @ouz-a

[nnethercote]

I stumbled across this while working on some changes to how errors are propagated to the outer levels of the compiler. In those changes I increased the number of normal errors that trigger a FatalError panic, which caused tests/ui-fulldeps/stable-mir/compilation-result.rs to fail.

[oli-obk]

@bors r+ rollup

[bors]

📌 Commit e72e7e9 has been approved by oli-obk

It is now in the queue for this repository.