rustc_codegen_llvm: make sse4.2 imply crc32 for LLVM 14
This fixes compiling things like the `snap` crate after
https://reviews.llvm.org/D105462. I added a test that verifies the
additional attribute gets specified, and confirmed that I can build
cargo with both LLVM 13 and 14 with this change applied.
r? `@nagisa` cc `@nikic`