Rollup merge of #139809 - alexcrichton:wasm-simd-safe, r=RalfJung

Don't warn about `v128` in wasm ABI transition

The `-Zwasm-c-abi=spec` mode of `extern "C"` does not actually change the meaning of `v128`  meaning that the FCW lint firing is a false positive.

cc rust-lang/rust#138762 (comment)

Author: matthiaskrgr