Allow uuid on wasm32 and wasi

[youknowone]

cc @lastmjs

python/cpython#104397

[lastmjs]

I wonder if _signal will be a dependency of other modules though, since signal depends on _signal. This just came up when including uuid.

[lastmjs]

It worked for uuid though!

[youknowone]

It will be eventually need to be implemented.
platform unnecessarily requires subprocess. and subprocess requires signal.
If you find any problem with platform, It can be also quickly patched.
signal module will take time