Factor out platforms for which libc is empty

[gnzlbg]

This change shouldn't change any functionality. It just separates the platforms for which libc is currently empty (only wasm32-unknown-unknown), from those for which it isn't. This is a non-functional change.

[rust-highfive]

r? @alexcrichton

(rust_highfive has picked a reviewer for you, use r? to override)

[gnzlbg]

Note that libc does not export c_void for wasm32-unknown-unknown, and that c_void is part of libcore.

[alexcrichton]

r=me, but looks like ci may be broken?

We'll fix this eventually for wasm32-unknown-unknown once the Clang ABI stabilizes and/or is released, but until that time we're gonna leave this as empty

[gnzlbg]

Yes, so summarizing the conversation from IRC, libc should always compile for all targets, but it should be empty for targets without a libc (or similar).

That is, wasm32-unknown-unknown would check that box at the moment (we can change that in the future), and the target_env = "none" targets would do so as well.

So i'm going to keep this PR more or less as is until its merged, but at some point we might want to go from explicitly listing the non-supported target, to "somehow" only have items in the supported targets and be empty by default.

[bors]

☔ The latest upstream changes (presumably #1127) made this pull request unmergeable. Please resolve the merge conflicts.

[gnzlbg]

@bors: r+

[bors]

📌 Commit d145731 has been approved by gnzlbg

[bors]

⌛ Testing commit d145731 with merge 16f6fef...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: gnzlbg
Pushing 16f6fef to master...

[alexcrichton]

I think this unfortunately breaks compilation of the wasm target in upstream rust-lang/rust, it turns out that the #![cfg] on the crate also removes the attributes of the crate! You can see that via:

// foo.rs
#![feature(no_core)]
#![no_core]
#![cfg(foo)]

compiled with

$ rustc foo.rs --crate-type lib --target x86_64-pc-windows-msvc
error[E0463]: can't find crate for `std`
  |
  = note: the `x86_64-pc-windows-msvc` target may not be installed

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.

(it shouldn't try to link std)

[alexcrichton]

I believe #1129 fixes that though

[gnzlbg]

I believe #1129 fixes that though

Damn, I'm so sorry. I was just going to ask whether that PR fixes it.

[alexcrichton]

No worries! I had no idea about this as well :)

[gnzlbg]

I'm trying to get rust-semverver up to a point that can be used to detect breaking changes to libc.