Add a flag to hir and ty TypeParameterDef and raise an error when using
explicit type parameters when calling a function using impl Trait in
argument position.

This reduces the size of hir::Expr from 128 to 88 bytes (!) and shaves
200MB out of #36799.

incr.comp.: Already hash HIR bodies during metadata export so they don't have to be hashed in downstream crates.

- Don't hash traits in scope as part of HIR hashing any more.
- Some queries returned DefIndexes from other crates.
- Provide a generic way of stably hashing maps (not used everywhere yet).

This PR kicks off the implementation of the [default binding modes RFC][1] by
introducing the `pat_binding_modes` typeck table mentioned in the [mentoring
instructions][2].

`pat_binding_modes` is populated in `librustc_typeck/check/_match.rs` and
used wherever the HIR would be scraped prior to this PR. Unfortunately, one
blemish, namely a two callers to `contains_explicit_ref_binding`, remains.
This will likely have to be removed when the second part of [1], the
`pat_adjustments` table, is tackled. Appropriate comments have been added.

See #42640.

[1]: https://github.com/rust-lang/rfcs/pull/2005
[2]: https://github.com/rust-lang/rust/issues/42640#issuecomment-313535089

No need to be mixed!

    pr review

Windows builder croaked. This change tries to fix that by actually
calling the global_asm-defined function so the symbol doesn't get
optimized away, if that is in fact what was happening.

Additionally, we provide an empty main() for non-x86 arches.

This initial commit provides implementations for HIR, MIR, and
everything that also needs to be supported for those two.