fix handling the default config for profiler and sanitizers

[12101111]

#78354 don't handle the case that user don't add any target-specific config in [target.*] of config.toml:

changelog-seen = 2
[llvm]
link-shared = true
[build]
sanitizers = true
profiler = true
[install]
[rust]
[dist]

The previes code handle the default config in Config::prase():

target.sanitizers = cfg.sanitizers.unwrap_or(build.sanitizers.unwrap_or_default());
target.profiler = cfg.profiler.unwrap_or(build.profiler.unwrap_or_default());
config.target_config.insert(TargetSelection::from_user(&triple), target);

In this case, toml.target don't contain any target, so the above code won't execute. Instead, a default Target is insert in

rust/src/bootstrap/sanity.rs

Lines 162 to 166 in c919f49

	build
	.config
	.target_config
	.entry(target.clone())
	.or_insert(Target::from_triple(&target.triple));

The default value for bool is false, hence the issue in #79124

This fix change the type of sanitizers and profiler to Option<bool>, so the default value is None, and fallback config is handled in Config::sanitizers_enabled and Config::profiler_enabled

fix #79124

cc @Mark-Simulacrum @richkadel

[rust-highfive]

r? @Mark-Simulacrum

(rust_highfive has picked a reviewer for you, use r? to override)

[Mark-Simulacrum]

@bors r+

Thanks!

[bors]

📌 Commit 36972b0 has been approved by Mark-Simulacrum