Rollup merge of #132552 - taiki-e:sparc-target-feature, r=workingjubilee

Add v9, v8plus, and leoncasa target feature to sparc and use v8plus in create_object_file

This adds the following three unstable target features:

- `v9`: SPARC-V9 instructions ([LLVM definition][sparc-v9])
  - Relevant to https://github.com/rust-lang/rust/pull/131222#issuecomment-2453310963
  - Relevant to https://github.com/rust-lang/rust/pull/132472#discussion_r1832606081
  - This is also needed to implement https://github.com/taiki-e/atomic-maybe-uninit/pull/31 (depends on inline assembly support) more robustly.
- `v8plus`: SPARC-V8+ ABI ([LLVM definition][sparc-v8plus])
  - This is added in LLVM 20. In LLVM 19 and older, it is emulated to work the same way as LLVM in each LLVM version.
  - See https://github.com/rust-lang/rust/issues/132585#issuecomment-2453926257 for more.
- `leoncasa`: CASA instruction[^1] of LEON3 and LEON4 processors ([LLVM definition][sparc-leoncasa], LLVM feature name: `hasleoncasa`)
  - This is needed to implement https://github.com/taiki-e/atomic-maybe-uninit/pull/31 (depends on inline assembly support) more robustly.

[^1]: Atomic CAS instruction

[sparc-v9]: f5e4ffaa49/llvm/lib/Target/Sparc/Sparc.td (L37-L39)
[sparc-v8plus]: f5e4ffaa49/llvm/lib/Target/Sparc/Sparc.td (L37-L39)
[sparc-leoncasa]: https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Sparc/LeonFeatures.td#L32-L37

compiler/rustc_span/src/symbol.rs

@@ -1867,6 +1867,7 @@ symbols! {
         slice_patterns,
         slicing_syntax,
         soft,
+        sparc_target_feature,
         specialization,
         speed,
         spotlight,
@@ -2109,6 +2110,7 @@ symbols! {
         usize_legacy_fn_max_value,
         usize_legacy_fn_min_value,
         usize_legacy_mod,
+        v8plus,
         va_arg,
         va_copy,
         va_end,