Added substring searching benchmarks.

test str::bench::bench_contains_bad_naive                   ... bench:      1309 ns/iter (+/- 36)
test str::bench::bench_contains_equal                       ... bench:       137 ns/iter (+/- 2)
test str::bench::bench_contains_short_long                  ... bench:      5473 ns/iter (+/- 14)
test str::bench::bench_contains_short_short                 ... bench:        57 ns/iter (+/- 6)
Switched to the two-way algorithm for string searching

test str::bench::bench_contains_bad_naive                   ... bench:       300 ns/iter (+/- 12)     from 1309 ns/iter (+/- 36)
test str::bench::bench_contains_equal                       ... bench:       154 ns/iter (+/- 7)      from  137 ns/iter (+/- 2)
test str::bench::bench_contains_short_long                  ... bench:      2998 ns/iter (+/- 74)     from 5473 ns/iter (+/- 14)
test str::bench::bench_contains_short_short                 ... bench:        65 ns/iter (+/- 2)      from   57 ns/iter (+/- 6)
debuginfo: Represent SIMD types as tuple structs instead of as fixed-sized arrays
rustc: Fix shadowing private import with reexport

The reexport didn't switch the privacy, so the reexport was actually considered
private, erroneously failing to resolve imports later on.

Closes #14082
guide-pointers: minor nits
rustc: Stop calling error! in resolve

These are taken care of with compiler errors later on, no need to spam with
extra unformatted information unconditionally.

Closes #14225
Optimize and fix time::precise_time_ns() on macos

Use sync::one::Once to fetch the mach_timebase_info only once when
running precise_time_ns(). This helps because mach_timebase_info() is
surprisingly inefficient. Also fix the order of operations when applying
the timebase to the mach absolute time value.

This improves the time on my machine from

```
test tests::bench_precise_time_ns ... bench:       157 ns/iter (+/- 4)
```

to

```
test tests::bench_precise_time_ns ... bench:        38 ns/iter (+/- 3)
```

and it will get even faster once #14174 lands.
auto merge of #14135 : gereeter/rust/two-way-search, r=brson

This changes the previously naive string searching algorithm to a two-way search like glibc, which should be faster on average while still maintaining worst case linear time complexity. This fixes #14107. Note that I don't think this should be merged yet, as this is the only approach to speeding up search I've tried - it's worth considering options like Boyer-Moore or adding a bad character shift table to this. However, the benchmarks look quite good so far:

    test str::bench::bench_contains_bad_naive                   ... bench:       290 ns/iter (+/- 12)     from 1309 ns/iter (+/- 36)
    test str::bench::bench_contains_equal                       ... bench:       479 ns/iter (+/- 10)     from  137 ns/iter (+/- 2)
    test str::bench::bench_contains_short_long                  ... bench:      2844 ns/iter (+/- 105)    from 5473 ns/iter (+/- 14)
    test str::bench::bench_contains_short_short                 ... bench:        55 ns/iter (+/- 4)      from   57 ns/iter (+/- 6)

Except for the case specifically designed to be optimal for the naive case (`bench_contains_equal`), this gets as good or better performance as the previous code.
rustc: Stop leaking enum variants into children

This plugs a leak where resolve was treating enums defined in parent modules as
in-scope for all children modules when resolving a pattern identifier. This
eliminates the code path in resolve entirely.

If this breaks any existing code, then it indicates that the variants need to be
explicitly imported into the module.

Closes #14221

[breaking-change]
auto merge of #14216 : kballard/rust/macos_precise_time_ns, r=alexcrichton

Use sync::one::Once to fetch the mach_timebase_info only once when
running precise_time_ns(). This helps because mach_timebase_info() is
surprisingly inefficient. Also fix the order of operations when applying
the timebase to the mach absolute time value.

This improves the time on my machine from

```
test tests::bench_precise_time_ns ... bench:       157 ns/iter (+/- 4)
```

to

```
test tests::bench_precise_time_ns ... bench:        38 ns/iter (+/- 3)
```

and it will get even faster once #14174 lands.
term: Don't run the code example, just compile it

This is blocking a snapshot because apparently the test fails on the bots.
auto merge of #14257 : alexcrichton/rust/fix-snap, r=huonw

This is blocking a snapshot because apparently the test fails on the bots.
auto merge of #14236 : alexcrichton/rust/issue-14082, r=brson

The reexport didn't switch the privacy, so the reexport was actually considered
private, erroneously failing to resolve imports later on.

Closes #14082
auto merge of #14224 : michaelwoerister/rust/simd-update, r=alexcrichton

This is a small change that improves the DWARF description of SIMD types by exposing their type name to debuginfo.
auto merge of #14239 : alexcrichton/rust/issue-14225, r=huonw

These are taken care of with compiler errors later on, no need to spam with
extra unformatted information unconditionally.

Closes #14225
auto merge of #14247 : Ryman/rust/minor_ptr_nit, r=alexcrichton

Not too hot on the second change, welcome a better suggestion/wording.
auto merge of #14253 : alexcrichton/rust/issue-14221, r=pcwalton

This plugs a leak where resolve was treating enums defined in parent modules as
in-scope for all children modules when resolving a pattern identifier. This
eliminates the code path in resolve entirely.

If this breaks any existing code, then it indicates that the variants need to be
explicitly imported into the module.

Closes #14221