[feature request] support -msimd128 argument

[deepkolos]

clang++ supports wasm simd v128 feature, but seem cheerp doesn't

D:\DEV\study\study-log-cpp\cheerp-demo
$ C:\cheerp\bin\clang++ -target cheerp -cheerp-linear-heap-size=128 js-export.cpp -o js-export.js -cheerp-pretty-code -msimd128
clang++.exe: warning: argument unused during compilation: '-msimd128' [-Wunused-command-line-argument]
warning: webMain or main entry point not found
warning: webMain or main entry point not found

[yuri91]

We have experimental support for simd in Cheerp 3.0.
In order to enable it you need to pass the command line option -cheerp-wasm-enable=simd though, not -msimd128.