Turn off Vectorization for Emscripten
Turn off Vectorization for Emscripten

When targeting Emscripten, rustc emits Vector Instructions by default.
However Web Assembly doesn't support Vector Instructions yet, which
causes Binaryen to fail converting the intermediate asm.js code to Web
Assembly. While asm.js kind of supports Vector Instructions, they
aren't supported by any browser other than Firefox, often meaning that
they need to be emulated very slowly. So it should just be turned off
for all Emscripten targets.

Fixes #38558

GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust