This helps with the specific problem described in rust-lang#49541, obviously without
making any large change to how inlining works in the general case.

Everything involved in the conversions is made `#[inline]`, except for the
`<Vec<T>>::into_boxed_slice` entry point which is made `#[inline(always)]`
after checking that duplicating the function mentioned in the issue prevented
its inlining if I only annotate it with `#[inline]`.

For the record, that function was:

```rust
pub fn foo() -> Box<[u8]> {
    vec![0].into_boxed_slice()
}
```

To help the inliner's job, we also hoist a `self.capacity() != self.len` check
in `<Vec<T>>::shrink_to_fit` and mark it as `#[inline]` too.

The Box::new(mem::uninitialized()) pattern actually actively copies
uninitialized bytes from the stack into the box, which is a waste of
time. Using the box syntax instead avoids the useless copy.

Debugging information for the extended tools is currently disabled for
concerns about the size.  This patch adds `--enable-debuginfo-tools` to
let one opt into having that debuginfo.

This is useful for debugging the tools in distro packages.  We always
strip debuginfo into separate packages anyway, so the extra size is not
a concern in regular use.

As discussed in rust-lang#15536, the LLVM documentation incorrect described
overflowing f64->f32 casts as being undefined behavior. LLVM never
treated them as such, and the documentation has been adjusted in
https://reviews.llvm.org/rL329065. As such, this warning can now
be removed.

Closes rust-lang#49622.

Inline most of the code paths for conversions with boxed slices

This helps with the specific problem described in rust-lang#49541, obviously without making any large change to how inlining works in the general case.

Everything involved in the conversions is made `#[inline]`, except for the `<Vec<T>>::into_boxed_slice` entry point which is made `#[inline(always)]` after checking that duplicating the function mentioned in the issue prevented its inlining if I only annotate it with
`#[inline]`.

For the record, that function was:

```rust
pub fn foo() -> Box<[u8]> {
    vec![0].into_boxed_slice()
}
```

To help the inliner's job, we also hoist a `self.capacity() != self.len` check in `<Vec<T>>::shrink_to_fit` and mark it as `#[inline]` too.

Prevent broken pipes causing ICEs

As the private `std::io::print_to` panics if there is an I/O error, which is used by `println!`, the compiler would ICE if one attempted to use a broken pipe (e.g. `rustc --help | false`). This introduces a new (private) macro `try_println!` which allows us to avoid this.

As a side note, it seems this macro might be useful publicly (and actually there seems to be [a crate specifically for this purpose](https://crates.io/crates/try_print/)), though that can probably be left for a future discussion.

One slight alternative approach would be to simply early exit without an error (i.e. exit code `0`), which [this comment](rust-lang#34376 (comment)) suggests is the usual approach. I've opted not to take that approach initially, because I think it's more helpful to know when there is a broken pipe.

Fixes rust-lang#34376.

…richton

Use box syntax instead of Box::new in Mutex::remutex on Windows

The Box::new(mem::uninitialized()) pattern actually actively copies
uninitialized bytes from the stack into the box, which is a waste of
time. Using the box syntax instead avoids the useless copy.

…e feature list

These are already stabilized in 1.26.

Fix incorrect span in `&mut` suggestion

Fixes rust-lang#49859

…ulacrum

rustbuild: allow building tools with debuginfo

Debugging information for the extended tools is currently disabled for
concerns about the size.  This patch adds `--enable-debuginfo-tools` to
let one opt into having that debuginfo.

This is useful for debugging the tools in distro packages.  We always
strip debuginfo into separate packages anyway, so the extra size is not
a concern in regular use.

Remove warning about f64->f32 cast being potential UB

As discussed in rust-lang#15536, the LLVM documentation incorrect described overflowing f64->f32 casts as being undefined behavior. LLVM never treated them as such, and the documentation has been adjusted in https://reviews.llvm.org/rL329065. As such, this warning can now be removed.

Closes rust-lang#49622.

---

I could not find any existing test checking for this warning. Should I be adding a test for the absence of the warning instead?

…tMisdreavus

Remove unnecessary indentation in rustdoc book codeblock.

None

Remove `underscore_lifetimes` and `match_default_bindings` from active feature list

These are already stabilized in 1.26.