Bootstrap: Check validity of `--target` and `--host` triples before starting a build
Resolves #122128
As described in the issue, validating the `target` and `host` triples would save a lot of time before actually starting a build. This would also check for custom targets by looking for a valid JSON spec if the specified target does not exist in the [supported](42825768b1/compiler/rustc_target/src/spec/mod.rs (L1401-L1689)
) list of targets.
This directory contains some source code for the Rust project, including:
- The bootstrapping build system
- Various submodules for tools, like cargo, tidy, etc.
For more information on how various parts of the compiler work, see the rustc dev guide.