Stabilize `sse4a` and `tbm` target features
This PR stabilizes the feature flag `sse4a_target_feature` and `tbm_target_feature` (tracking issue rust-lang/rust#44839).
# Public API
The 2 `x86` target features `sse4a` and `tbm`
Also, these were added in LLVM2.6 and LLVM3.4-rc1, respectively, and as the minimum LLVM required for rustc is LLVM19, we are safe in that front too!
As all of the required tasks have been done (adding the target features to rustc, implementing their runtime detection in std_detect and implementing the associated intrinsics in core_arch), these target features can be stabilized now. The intrinsics were stabilized *long* ago, in 1.27.0
Reference PR:
- https://github.com/rust-lang/reference/pull/1949
cc `@rust-lang/lang`
`@rustbot` label I-lang-nominated
r? lang
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