3 MLIR tests `FAIL` on SPARC, both Solaris/sparcv9 and Linux/sparc64:
```
MLIR :: Conversion/ArithToSPIRV/arith-to-spirv-le-specific.mlir
MLIR :: IR/elements-attr-interface.mlir
MLIR :: Target/LLVMIR/llvmir-le-specific.mlir
```
The issue is always the same: the tests in question are
little-endian-only currently, so this patch `XFAIL`s them on `sparc*` as
is already done for `s390x`.
Tested on `sparcv9-sun-solaris2.11`, `sparc64-unknown-linux-gnu`,
`amd64-pc-solaris2.11`, and `x86_64-pc-linux-gnu`.