Enable `#[cfg(target_thread_local)]`

[ian-h-chamberlain]

This is falling out from the discussion in rust3ds/pthread-3ds#13

Based on rust-lang#91659 – many targets default to false for has_thread_local, including armv6k-nintendo-3ds. Based on our testing #[thread_local] does work on this platform, and as someone pointed out it appears all ARM targets actually support the #[thread_local] attribute.

I think we should add has_thread_local: true to take advantage of the "fast" thread-local support builtin to std: https://github.com/Meziu/rust-horizon/blob/horizon-std/library/std/src/thread/mod.rs#L186

I can do it (trivial change) but I wanted to make sure everyone's on board before submitting a PR to update the target. I'm building a local version of the compiler to test as well.

[AzureMarker]

Sounds good, open a PR and we can test and discuss there too.

[AzureMarker]

This was merged into upstream in rust-lang#95341
(I don't have permission to close this issue myself)