Closes rust-lang#13546 (workcache: Don't assume gcc exists on all platforms)
Closes rust-lang#13545 (std: Remove pub use globs)
Closes rust-lang#13530 (test: Un-ignore smallest-hello-world.rs)
Closes rust-lang#13529 (std: Un-ignore some float tests on windows)
Closes rust-lang#13528 (green: Add a helper macro for booting libgreen)
Closes rust-lang#13526 (Remove RUST_LOG="::help" from the docs)
Closes rust-lang#13524 (dist: Make Windows installer uninstall first. Closes rust-lang#9563)
Closes rust-lang#13521 (Change AUTHORS section in the man pages)
Closes rust-lang#13519 (Update GitHub's Rust projects page.)
Closes rust-lang#13518 (mk: Change windows to install from stage2)
Closes rust-lang#13516 (liburl doc: insert missing hyphen)
Closes rust-lang#13514 (rustdoc: Better sorting criteria for searching.)
Closes rust-lang#13512 (native: Fix a race in select())
Closes rust-lang#13506 (Use the unsigned integer types for bitwise intrinsics.)
Closes rust-lang#13502 (Add a default impl for Set::is_superset)

…gation-resolution, r=lnicola

Apply fallback before final obligation resolution

Fixes rust-lang#13249
Fixes rust-lang#13518

We've been applying fallback to type variables independently even when there are some unresolved obligations that associate them. This PR applies fallback to unresolved scalar type variables before the final attempt of resolving obligations, which enables us to infer more.

Unlike rustc, which has separate storages for each kind of type variables, we currently don't have a way to retrieve only integer/float type variables without folding/visiting every single type we've inferred. I've repurposed `TypeVariableData` as bitflags that also hold the kind of the type variable it's referring to so that we can "reconstruct" scalar type variables from their indices.

This PR increases the number of ??ty for rust-analyzer repo not because we regress and fail to infer the existing code but because we fail to infer the new code. It seems we have problems inferring some functions bitflags produces.