The Windows dist builders are the slowest builders right now, and the
distribution phase of them is enormously slow clocking in at around 20
minutes to build all the related installers. This commit starts to
optimize these by turning down the compression level in the `exe`
installers. These aren't super heavily used so there's no great need for
them to be so ultra-compressed, so let's dial back the compression
parameters to get closer to the rest of our xz archives. This brings the
installer in line with the gz tarball installer locally, and also brings
the compression settings on par with the rest of our xz installers.

This is the same as rust-lang#64615 except applied to our MSI installers. The
same fix is applied effectively bringing these installers in line with
the gz tarball installers, which are about 3x faster to produce locally
and likely much faster to produce on CI.

* Pass `/Q` to `iscc` on Windows to supress the thousands of lines of
  output about compressing documentation.
* Print out what's happening before long steps
* Use `timeit` to print out timing information for long-running
  installer assemblies.

fix rust-lang#63983

The mentioned Cargo test is fixed in rust-lang/cargo#7210

…-obk

Add explanation to type mismatch involving type params and assoc types

CC rust-lang#63711

…mulacrum

rustbuild: Turn down compression on exe installers

The Windows dist builders are the slowest builders right now, and the
distribution phase of them is enormously slow clocking in at around 20
minutes to build all the related installers. This commit starts to
optimize these by turning down the compression level in the `exe`
installers. These aren't super heavily used so there's no great need for
them to be so ultra-compressed, so let's dial back the compression
parameters to get closer to the rest of our xz archives. This brings the
installer in line with the gz tarball installer locally, and also brings
the compression settings on par with the rest of our xz installers.

…mulacrum

rustbuild: Turn down compression on msi installers

This is the same as rust-lang#64615 except applied to our MSI installers. The
same fix is applied effectively bringing these installers in line with
the gz tarball installers, which are about 3x faster to produce locally
and likely much faster to produce on CI.

…=Mark-Simulacrum

rustbuild: Improve output of `dist` step

* Pass `/Q` to `iscc` on Windows to supress the thousands of lines of
  output about compressing documentation.
* Print out what's happening before long steps
* Use `timeit` to print out timing information for long-running
  installer assemblies.
* Try to scope output of `Dist ...` to not also encompass actual build steps

Fixes rust-lang#63962. Hint about missing tuple parentheses in patterns

Update to LLVM 9.0.0

Allow using fn pointers in const fn with unleash miri

This allows using function pointers in const fns  when `-Zunleash-the-miri-within-you` is enabled.

If the call to the `const fn` happens in a `const`-context, the function pointer is required to point to a `const fn`:

```rust
fn non_const_fn() -> i32 { 42 }
const fn const_fn() -> i32 { 42 }
const fn foo(x: fn() -> i32) -> i32 { x() }

let x: i32 = foo(non_const_fn_ptr); // OK
let y: i32 = foo(const_fn_ptr); // OK
const X: i32 = foo(non_const_fn_ptr); // ERROR: `non_const_fn` is not `const fn`
const Y: i32 = foo(const_fn_ptr); // OK
```

r? @oli-obk

…ct, r=estebank

unify errors for tuple/struct variants

fix rust-lang#63983

…Simulacrum

fully remove AstBuilder

The mentioned Cargo test is fixed in rust-lang/cargo#7210

I think this can be removed now?