Remove runtime failure from pattern matching

It's an artifact of the old refutable version of `match`
and is no longer necessary.
Lexer; subtly wrong; no makefile
Add raw string literal ambiguity document
First pass at line comment correctness
Refine the tooling, handle comments
Byte/raw binary literal fixes
ignore-lexer-test to broken files and remove some tray hyphens

I blame @ChrisMorgan for the hyphens.
Allow merging of statics generated by format!()
auto merge of #15700 : jakub-/rust/match-fail-removal, r=pcwalton

It's an artifact of the old refutable version of `match` and is no longer necessary.
Use fewer instructions for `fail!`

Adds a special-case fail function, rustrt::unwind::begin_unwind_no_time_to_explain,
that encapsulates the printing of the words "explicit failure".

The before/after optimized assembly:

```
        leaq    "str\"str\"(1369)"(%rip), %rax
        movq    %rax, 8(%rsp)
        movq    $19, 16(%rsp)
        leaq    8(%rsp), %rdi
        movl    $11, %esi
        callq   _ZN6unwind31begin_unwind_no_time_to_explain20hd1c720cdde6a116480dE@PLT
```

```
        leaq    "str\"str\"(1412)"(%rip), %rax
        movq    %rax, 24(%rsp)
        movq    $16, 32(%rsp)
        leaq    "str\"str\"(1413)"(%rip), %rax
        movq    %rax, 8(%rsp)
        movq    $19, 16(%rsp)
        leaq    24(%rsp), %rdi
        leaq    8(%rsp), %rsi
        movl    $11, %edx
        callq   _ZN6unwind12begin_unwind21h15836560661922107792E
```

Before/after filesizes:

rwxrwxr-x 1 brian brian 21479503 Jul 20 22:09 stage2-old/lib/librustc-4e7c5e5c.so
rwxrwxr-x 1 brian brian 21475415 Jul 20 22:30 x86_64-unknown-linux-gnu/stage2/lib/librustc-4e7c5e5c.so
Update LLVM to address an issue with range metadata in hoisted loads

Fixes #15793.
Moved `syntax::ext::base::SyntaxEnv` into `syntax::ext::base::ExtCtx`
Fix rustdoc --passes list

Allow "rustdoc --passes list" to work without specifying input files,
as shown in the examples section of the man page.
Refactoring: Only use `MacroExpander` for expanding outside of
`syntax::ext::expand`
Clarify range's exclusivity.

Inspired by http://www.reddit.com/r/rust/comments/298js2/what_is_the_rationale_behind_the_second_parameter/
Guide: fix headings
auto merge of #15217 : steveklabnik/rust/range, r=huonw

Inspired by http://www.reddit.com/r/rust/comments/298js2/what_is_the_rationale_behind_the_second_parameter/
lexer tests: makefile/configure
Break apart long lines in verify.rs
Shuffle around check-lexer conditions