Auto merge of #77298 - jyn514:bootstrap-config, r=Mark-Simulacrum
Auto merge of #77298 - jyn514:bootstrap-config, r=Mark-Simulacrum

Don't warn if the config file is somewhere other than `config.toml`

Previously, `config.config` was always hardcoded as `"config.toml"`.
I thought that it was being overridden with the actual value later, but
it turns out `flags.config` was being completely discarded. This keeps
`config.config` in sync with `flags.config`.

Fixes https://github.com/rust-lang/rust/issues/77293
r? `@Mark-Simulacrum`
cc `@davidtwco`

graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust