mk: Move from `-D warnings` to `#![deny(warnings)]`

[alexcrichton]

This commit removes the -D warnings flag being passed through the makefiles to
all crates to instead be a crate attribute. We want these attributes always
applied for all our standard builds, and this is more amenable to Cargo-based
builds as well.

Note that all deny(warnings) attributes are gated with a cfg(stage0)
attribute currently to match the same semantics we have today

[rust-highfive]

r? @brson

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

[alexcrichton]

One change I also noticed was that the rustc_mir crate did not previously have an #[unstable] tag, which means that this compiles in stable Rust:

extern crate rustc_mir;

fn main() {}

I added the #[unstable] tag here, but I would be quite surprised if that actually caused breakage. @brson do you think it's worth adding to relnotes?

[brson]

@alexcrichton It may not be worth mentioning but I'll tag it and think about it later. Also nominating for beta, maybe just the rustc_mir crate fix.

Here's an issue to lint for this problem: #31122

[alexcrichton]

Oh let me rearrange the commits for the new unstable attribute to be in its own commit to be easily cherry-picked in that case.

[alexcrichton]

rearranged

[brson]

@bors r+

[bors]

📌 Commit 3a107c5 has been approved by brson

[bors]

⌛️ Testing commit 3a107c5 with merge 234e3dd...

[bors]

💔 Test failed - auto-mac-64-opt

[alexcrichton]

@bors: r=brson ae8f816

[bors]

⌛️ Testing commit ae8f816 with merge 96b734f...

[bors]

💔 Test failed - auto-linux-64-x-android-t

[bors]

☔️ The latest upstream changes (presumably #31148) made this pull request unmergeable. Please resolve the merge conflicts.

[alexcrichton]

@bors: r=brson fc8d780

[bors]

⌛️ Testing commit fc8d780 with merge 5ead8cf...

[bors]

💔 Test failed - auto-linux-64-x-android-t

[alexcrichton]

@bors: r=brson cc4db8b

[alexcrichton]

@bors: r=brson 790b862

[tamird]

travis failed btw

src/libstd/process.rs:849:5: 866:6 error: duplicate definition of value `test_inherit_env` [E0428]
src/libstd/process.rs:849     fn test_inherit_env() {
src/libstd/process.rs:850         use env;
src/libstd/process.rs:851 
src/libstd/process.rs:852         let mut result = env_cmd().output().unwrap();
src/libstd/process.rs:853         let output = String::from_utf8(result.stdout).unwrap();
src/libstd/process.rs:854 
                          ...
src/libstd/process.rs:849:5: 866:6 help: run `rustc --explain E0428` to see a detailed explanation
src/libstd/process.rs:829:5: 845:6 note: first definition of value `test_inherit_env` here
src/libstd/process.rs:829     fn test_inherit_env() {
src/libstd/process.rs:830         use env;
src/libstd/process.rs:831 
src/libstd/process.rs:832         let result = env_cmd().output().unwrap();
src/libstd/process.rs:833         let output = String::from_utf8(result.stdout).unwrap();
src/libstd/process.rs:834 

[tamird]

shouldn't this not be ignored on android?

[alexcrichton]

@bors: r=brson 9d95a22

[bors]

⌛️ Testing commit 9d95a22 with merge 2518a71...

[bors]

💔 Test failed - auto-win-msvc-64-opt

[alexcrichton]

@bors: r=brson cdc1c2c

[bors]

⌛️ Testing commit cdc1c2c with merge 669130e...

[bors]

💔 Test failed - auto-mac-64-nopt-t

[alexcrichton]

@bors: r=brson cb343c3

[bors]

⌛️ Testing commit cb343c3 with merge 4b61585...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt

[alexcrichton]

flagging as beta-accepted, but only the commit alexcrichton@4b3c355