Removed unnecessary arguments for walk_* functions
Implement set complement and universe for bitflags
auto merge of #14192 : pongad/rust/walkcleanup, r=pcwalton

Fixes #14134
auto merge of #14009 : jcmoyer/rust/bitflags-complement, r=alexcrichton

I feel that this is a very vital, missing piece of functionality. This adds on to #13072.

Only bits used in the definition of the bitflag are considered for the universe set. This is a bit safer than simply inverting all of the bits in the wrapped value.

```rust
bitflags!(flags Flags: u32 {
    FlagA       = 0x00000001,
    FlagB       = 0x00000010,
    FlagC       = 0x00000100,
    FlagABC     = FlagA.bits
                | FlagB.bits
                | FlagC.bits
})

...

// `Not` implements set complement
assert!(!(FlagB | FlagC) == FlagA);
// `all` and `is_all` are the inverses of `empty` and `is_empty`
assert!(Flags::all() - FlagA == !FlagA);
assert!(FlagABC.is_all());
```
rustc: Improve error messages for resolve failures.
auto merge of #14086 : Ryman/rust/resolve_error_suggestions, r=alexcrichton

Provides better help for the resolve failures inside an `impl` if the name matches:
- a field on the self type
- a method on the self type
- a method on the current trait ref (in a trait impl)

Not handling trait method suggestions if in a regular `impl` (as you can see on line 69 of the test), I believe it is possible though.

Also, provides a better message when `self` fails to resolve due to being a static method.

It's using some unsafe pointers to skip copying the larger structures (which are only used in error conditions); it's likely possible to get it working with lifetimes (all the useful refs should outlive the visitor calls) but I haven't really figured that out for this case. (can switch to copying code if wanted)

Closes #2356.
Fix typo, darwing => darwin
Add a flex reference lexer and build system stuff

This is the first half of lexer testing.