More defailbloating

With this, all the failure lang item calls, and all `begin_unwind` (`fail!`) calls are optimized to take either one or two pointers, at least one of which is a constant, with the exception that the bounds check lang item also takes `index` and `len`. Code gen for all that is gorgeous.

Divide-by-zero before:

```
        leaq    "str\"str\"(1762)"(%rip), %rax
        movq    %rax, 16(%rsp)
        movq    $27, 24(%rsp)
        leaq    "str\"str\"(1542)"(%rip), %rax
        movq    %rax, (%rsp)
        movq    $19, 8(%rsp)
        leaq    16(%rsp), %rdi
        leaq    (%rsp), %rsi
        movl    $32, %edx
        callq   _ZN7failure5fail_20hc04408f955ce60aaqWjE@PLT
```

After:

```
        leaq    .Lconst(%rip), %rdi
        callq   _ZN7failure5fail_20haf918a97c8f7f2bfqWjE@PLT
```

Bounds check before:

```
        leaq    "str\"str\"(1542)"(%rip), %rax
        movq    %rax, 8(%rsp)
        movq    $19, 16(%rsp)
        leaq    8(%rsp), %rdi
        movl    $38, %esi
        movl    $1, %edx
        movl    $1, %ecx
        callq   _ZN7failure17fail_bounds_check20hf4bc3c69e96caf41RXjE@PLT
```

Bounds check after:

```
        leaq    .Lconst2(%rip), %rdi
        movl    $1, %esi
        movl    $1, %edx
        callq   _ZN7failure17fail_bounds_check20h5267276a537a7de22XjE@PLT
```

Size before:

21277995 librustc-4e7c5e5c.s

```
text       data
12554881   6089335
```

Size after:

21247617 librustc-4e7c5e5c.so

```
text       data
12518497   6095748
```

The next two steps might be to change the amount of information we generate based on a compiler flag, and maybe debug levels; and to investigate improving codegen for `fmt::Arguments`, which appears in many `fail!` invocations.

r? @pcwalton