Make TyTrait embed a `TraitRef`, so that when we extend TraitRef, it naturally carries over to object types.

I wanted to embed an `Rc<TraitRef>`, but I was foiled by the current
static rules, which prohibit non-Sync values from being stored in
static locations. This means that the constants for `ty_int` and so
forth cannot be initialized.

1. Introduce `putpathvar` function that prints variable shell-quoted by using `%q` format specifier. This function is used within `probe` to save the result into `config.tmp`.
2. Removes search-and-replace pattern that transforms `\` into `/` as it messes up shell-quoted strings.

Closes #14197

Removes the `matchers` nonterminal.

If you're using `$foo:matchers` in a macro, write `$foo:tt` instead.

[breaking-change]

Assert at run time instead. Fixes #13756.

I’d rather have this be detected at compile-time, but I don’t know how to do that.

libs: add Deref, DerefMut impls for references, fixing a bug in compiler in the process that was blocking this.

r? @aturon 

Closes #16529

r? @aturon 

Fixes #18567. `Struct{x:foo, .. with_expr}` did not walk `with_expr`, which allowed
using moved variables in some cases.  The CFG for structs also built up with
`with_expr` happening before the fields, which is now reversed. (Fields are now
before the `with_expr` in the CFG)

libs: add Deref, DerefMut impls for references, fixing a bug in compiler in the process that was blocking this.

Fixes #18621.

Assert at run time instead. Fixes #13756.

I’d rather have this be detected at compile-time, but I don’t know how to do that.

* `from_str_radix_float` gives incorrect results for negative float strings. Changes the accumulator used to start at -0.0 instead of -1.0.
* Adds missing tests

Closes #16529

Fix by @Gankro!

To make progress on #18585 we're paring down the distribution to theoretically
"only libstd", and this commit makes progress on this by removing the rlibc
crate from the distribution.

The crate has now been moved into an external cargo package located in the rust
lang organization [1]. This is a breaking change due to this removal, and
existing crates depending on `rlibc` should use the Cargo crate instead.

[1]: https://github.com/rust-lang/rlibc

[breaking-change]
cc #18585