Add WebAssembly to core.stdc.config

[IDONTUSEGH]

Added a version(WebAssembly) block to provide the correct C compatible
type aliases.

This is a copy of the WASI block.

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[dkorpel]

When I added stdc definitions for WebAssembly, I was told that it's the C runtime (e.g. WASI) instead of the architecture (WASM) dictating C types: dlang/druntime#3848

Added a version(WebAssembly) block to provide the correct C compatible type aliases.

What source do you have for these definitions being correct for WebAssembly in general?

[IDONTUSEGH]

This is needed because LDC imports that module for ImportC.

WASI adopts the data model of the underlying WebAssembly architecture it is compiled for, hence why I copied the version block, and I confirmed with: https://github.com/WebAssembly/tool-conventions/blob/main/BasicCABI.md

The feedback on that PR refers to runtime specific libc definitions. My PR is the exception because it just defines the fundamental C types. I think yours would have been accepted if it'd have just been that.

[dkorpel]

That document says:

As mentioned in README, it's not the only possible C ABI. It is the ABI that the clang/LLVM WebAssembly backend is currently using, and any other C or C++ compiler wishing to be ABI-compatible with it.

[IDONTUSEGH]

It's the same story with the WASI aliases, I think it's fine.

ping @kinke @ibuclaw , do you think this is fine to have? Or should they be separate for GDC/LDC?

[dkorpel]

I also think it's fine to just assume LLVM backend conventions since there are no other D compilers targeting WebAssembly currently, but then we could also just replace the version (WASI) with version (WebAssembly) and add a comment about our assumption rather than copying the WASI block.

[ibuclaw]

If unsure, ask feedable in #gcc on OFTC, who's doing the gcc port. But otherwise likely nothing worth blocking.

[kinke]

Also note that version(WebAssembly) also applies to Emscripten targets, where other versions are predefined (Posix, linux, CRuntime_Musl), so please take care not to break those targets.

[kinke]

For clarity, here for this PR, I suggest simply renaming the existing WASI block to WebAssembly, ideally including a link to https://github.com/WebAssembly/tool-conventions/blob/main/BasicCABI.md#data-representation. It's a copy of the earlier Posix block anyway, and GCC has its own leading version (GNU) block.