consider giving precedence to `--config` over RUST_BOOTSTRAP_CONFIG

[jyn514]

rust/src/bootstrap/bootstrap.py

Lines 1224 to 1228 in 7b43cfc

	# Read from `RUST_BOOTSTRAP_CONFIG`, then `--config`, then fallback to `config.toml` (if it
	# exists).
	toml_path = os.getenv('RUST_BOOTSTRAP_CONFIG') or args.config
	if not toml_path and os.path.exists('config.toml'):
	toml_path = 'config.toml'

It seems pretty strange to me that the env variable would take precedence over --config. It would be nice to switch the precedence.

cc @Mark-Simulacrum

Originally posted by @jyn514 in #92260 (comment)

[Mark-Simulacrum]

Added in #73317; it seems like it makes sense for --config to override, though probably not typically all that useful. Happy to see a PR, should be pretty easy so marking as such.

[mfrw]

@rustbot claim