Signed integers in C don't wrap around. That's undefined behavior. Unsigned integers behave modulo 2^n, so if you want wrap around in C you should be using unsigned integers. Any C compiler to WebAssembly would have to implement unsigned behavior regardless of the semantics of WebAssembly's native unsigned operations.

For information on the semantics of WebAssembly arithmetic, see

https://github.com/WebAssembly/design/blob/master/Semantics....

For other information about WebAssembly start here

https://github.com/WebAssembly/design/