Auto merge of #132472 - taiki-e:sparc-asm, r=Amanieu

Basic inline assembly support for SPARC and SPARC64

This implements asm_experimental_arch (tracking issue rust-lang/rust#93335) for SPARC and SPARC64.

This PR includes:

- General-purpose registers `r[0-31]` (`reg` register class, LLVM/GCC constraint `r`)
  Supported types: i8, i16, i32, i64 (SPARC64-only)
  Aliases: `g[0-7]` (`r[0-7]`), `o[0-7]` (`r[8-15]`), `l[0-7]` (`r[16-23]`), `i[0-7]` (`r[24-31]`)
- `y` register (clobber-only, needed for clobber_abi)
- preserves_flags: Integer condition codes (`icc`, `xcc`) and floating-point condition codes (`fcc*`)

The following are *not* included:

- 64-bit integer support on SPARC-V8+'s global or out registers (`g[0-7]`, `o[0-7]`): GCC's `h` constraint (it seems that there is no corresponding constraint in LLVM?)
- Floating-point registers (LLVM/GCC constraint `e`/`f`):
  I initially tried to implement this, but postponed it for now because there seemed to be several parts in LLVM that behaved differently than in the LangRef's description.
- clobber_abi: Support for floating-point registers is needed.

Refs:
- LLVM
  - Reserved registers /~https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Sparc/SparcRegisterInfo.cpp#L52
  - Register definitions /~https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Sparc/SparcRegisterInfo.td
  - Supported constraints https://llvm.org/docs/LangRef.html#supported-constraint-code-list
- GCC
  - Reserved registers /~https://github.com/gcc-mirror/gcc/blob/63b6967b06b5387821c4e5f2c113da6aaeeae2b7/gcc/config/sparc/sparc.h#L633-L658
  - Supported constraints https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html
- SPARC ISA/ABI
  - (64-bit ISA) The SPARC Architecture Manual, Version 9
    (32-bit ISA) The SPARC Architecture Manual, Version 8
    (64-bit ABI) System V Application Binary Interface SPARC Version 9 Processor Supplement, Rev 1.35
    (32-bit ABI) System V Application Binary Interface SPARC Processor Supplement, Third Edition
    The above docs can be downloaded from https://sparc.org/technical-documents
  - (32-bit V8+ ABI) The V8+ Technical Specification
    https://temlib.org/pub/SparcStation/Standards/V8plus.pdf

cc `@thejpster` (sparc-unknown-none-elf target maintainer)
(AFAIK, other sparc/sprac64 targets don't have target maintainers)

r? `@Amanieu`

`@rustbot` label +O-SPARC +A-inline-assembly