Rollup merge of #79155 - 12101111:fix-profiler-config, r=Mark-Simulacrum

Rollup merge of #79155 - 12101111:fix-profiler-config, r=Mark-Simulacrum

fix handling the default config for profiler and sanitizers

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

```rust
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 https://github.com/rust-lang/rust/blob/c919f490bbcd2b29b74016101f7ec71aaa24bdbb/src/bootstrap/sanity.rs#L162-L166

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`