@alexcrichton figured out a way how to do it :)

This fixes an optimization regression by allowing LLVM to see through more
functions.

Closes rust-lang#43272

Stabilizes:

* `<char>::escape_debug`
* `std::char::EscapeDebug`

Closes rust-lang#35068

Stabilized:

* `Option::get_or_insert`
* `Option::get_or_insert_with`

Closes rust-lang#39288

Stabilized

* `<str>::get`
* `<str>::get_mut`
* `<str>::get_unchecked`
* `<str>::get_unchecked_mut`

Closes rust-lang#39932

Stabilizes:

* `CString::as_c_str`
* `CString::into_boxed_c_str`
* `CStr::into_c_string`
* `OsString::into_boxed_os_str`
* `OsStr::into_os_string`
* `PathBuf::into_boxed_path`
* `PathBuf::into_path_buf`

Closes rust-lang#40380

Stabilizes:

* `Utf8Error::error_len`

Closes rust-lang#40494

Stabilizes

* `core::mem::ManuallyDrop`
* `std::mem::ManuallyDrop`
* `ManuallyDrop::new`
* `ManuallyDrop::into_inner`
* `ManuallyDrop::drop`
* `Deref for ManuallyDrop`
* `DerefMut for ManuallyDrop`

Closes rust-lang#40673

Stabilizes:

* `compile_error!` as a macro defined by rustc

Closes rust-lang#40872

Stabilizes

* `<&mut str>::as_bytes_mut`
* `<Box<str>>::into_boxed_bytes`
* `std::str::from_boxed_utf8_unchecked`
* `std::str::from_utf8_mut`
* `std::str::from_utf8_unchecked_mut`

Closes rust-lang#41119