Auto merge of #12276 - PartiallyTyped:hide-thread-local, r=blyxyas

Fix FP in `threadlocal!` when falling back to `os_local`

**Issue**: The lint always triggers for some targets.
**Why**: The lint assumes an `__init` function is not present for const initializers.
This does not hold for all targets. Some targets always have an initializer function.
**Fix**: If an initializer function exists, we check that it is not a `const` fn.

Lint overview before the patch:

1. Outside `threadlocal!`, then exit early.
2. In `threadlocal!` and `__init` does not exist => is const already, exit early.
3. In `threadlocal!` and `__init` exists and `__init` body can be `const` => we lint.

Lint overview after the patch:

1. Outside `threadlocal!`, then exit early.
2. In `threadlocal!` and `__init` does not exist => is const already, exit early.
3. In `threadlocal!` and `__init` exists and is `const fn` => is const already, exit early.
4. In `threadlocal!` and `__init` exists and is not `const fn` and `__init` body can be `const` => we lint.

The patch adds step 3.

changelog: Fixed fp in [`thread_local_initializer_can_be_made_const`] where fallback implementation of `threadlocal!` was always linted.

## Verifying the changes
For each of these platforms [ mac, x86_64-windows-gnu, x86_64-windows-msvc ]:

1. switched to master, ran bless. Found a failure for windows-gnu.
2. switched to patch, ran bless. Success for all three platforms.

## How platform affects the lint:

The compiler performs a [conditional compilation depending on platform features](https://doc.rust-lang.org/src/std/sys/common/thread_local/mod.rs.html). The `os_local` fallback includes a call to `__init`, without step 3, we lint in all cases.

```rust
cfg_if::cfg_if! {
    if #[cfg(any(all(target_family = "wasm", not(target_feature = "atomics")), target_os = "uefi"))] {
        #[doc(hidden)]
        mod static_local;
        #[doc(hidden)]
        pub use static_local::{Key, thread_local_inner};
    } else if #[cfg(target_thread_local)] {
        #[doc(hidden)]
        mod fast_local;
        #[doc(hidden)]
        pub use fast_local::{Key, thread_local_inner};
    } else {
        #[doc(hidden)]
        mod os_local;
        #[doc(hidden)]
        pub use os_local::{Key, thread_local_inner};
    }
}
```

r? `@llogiq`

0 files changed, 0 insertions, 0 deletions