[clang] [WebAssembly] Add tests for generic CPU config (PR #80775)

[Heejin Ahn via cfe-commits]

aheejin wrote:

Ah, I didn't notice there's `DEFAULT` tests in `wasm-features.c`... But more importantly, I noticed `wasm-features.c` tests don't work as intended anyway. I am planning to delete that test. So I'll make this PR just update the `wasm-target-features.c`.

https://github.com/llvm/llvm-project/pull/80775