Support wasm32-unknown-unknown

[pravdomil]

Now I see only support for emscripten, is there any plan for supporting target wasm32-unknown-unknown?

https://github.com/alexcrichton/cc-rs/blob/9e57a2b0e922a96be5d28b1adf6e5fc41d5d762c/src/lib.rs#L1696

[alexcrichton]

Ideally we would support this! The target, however, doesn't really have a C compiler because there's no real standard "sysroot" (currently) to actually compile C code against. The recently released clang 8.0 compiler though is the only one we'd also be compatible with on wasm32-unknown-unknown, so we could at least add that and rely on users to set the right CFLAGS to compile with the right headers/sysroot/etc

[pravdomil]

I'll be happy to use clang 8 for it.

[tanis2000]

I'm facing a similar problem here servo/rust-stb-image#94 but I have no clue where the wasm32 sysroot lives. I'm on CLANG 8.0.0 so I suppose it actually supports compiling to wasm32 but without the correct sysroot it can't find stdio.h and such headers.