Update documentation for from_raw_parts

Fixes #19269.
Lifetime guide -> ownership guide
impl Clone for Cow
getopts: cleanup, renames, remove reexports

* Remove public reexports, as a part of #19253
* Rename getopts::Fail_ to getopts::Fail
 * Didn't see a reason for the suffixed '_'
* Removed getopts::FailType
 * Looked like it was only beings used for tests; refactored the tests
   to stop requiring it
* A few other non-breaking trivial refactoring changes

[breaking-change]
impl Str for CowString

This implementation existed on MaybeOwned, but has been lost in the
transition to Cows. Let's put it back.
small doc fixes

We don't need this &mut, and vec could use []s
Add test for #18908
fix expand_quote_ty function as parse_ty was changed and needs no arguments now
Fix typo in reference.md
Replace some verbose match statements with their `if let` equivalent.

No semantic changes, no enabling `if let` where it wasn't already enabled.
syntax: Make `asm!` clobbers a proper vector.

Otherwise `--pretty expanded` diverges.
auto merge of #19365 : frewsxcv/rust/getopts-cleanup, r=alexcrichton

* Remove public reexports, as a part of #19253
* Rename getopts::Fail_ to getopts::Fail
 * Didn't see a reason for the suffixed '_'
* Removed getopts::FailType
 * Looked like it was only beings used for tests; refactored the tests
   to stop requiring it
* A few other non-breaking trivial refactoring changes

[breaking-change]
Adjust some error messages to start with a lowercase letter and not finish with a full stop
mk: Use host llvm linkage paths, not target ones

We only build LLVM for the host architecture, not the target architecture, so
this was just a minor typo in the parameters uses.

Closes #19383
Fix the ordering of `unsafe` and `extern` in methods

This breaks code that looks like this:

    trait Foo {
        extern "C" unsafe fn foo();
    }

    impl Foo for Bar {
        extern "C" unsafe fn foo() { ... }
    }

Change such code to look like this:

    trait Foo {
        unsafe extern "C" fn foo();
    }

    impl Foo for Bar {
        unsafe extern "C" fn foo() { ... }
    }

Fixes #19398.

[breaking-change]
Allow trailing commas in array patterns and attributes
trans: Eliminated redundant allocations.
auto merge of #19369 : seanmonstar/rust/cow-str, r=alexcrichton

This implementation existed on MaybeOwned, but has been lost in the
transition to Cows. Let's put it back.

@aturon r?
Simplify `RefCell` code a bit, make `deref` a no-op.
Fix typo in tests makefile