Rollup merge of #38699 - japaric:lsan, r=alexcrichton

Rollup merge of #38699 - japaric:lsan, r=alexcrichton

LeakSanitizer, ThreadSanitizer, AddressSanitizer and MemorySanitizer support

```
$ cargo new --bin leak && cd $_

$ edit Cargo.toml && tail -n3 $_
```

``` toml
[profile.dev]
opt-level = 1
```

```
$ edit src/main.rs && cat $_
```

``` rust
use std::mem;

fn main() {
    let xs = vec![0, 1, 2, 3];
    mem::forget(xs);
}
```

```
$ RUSTFLAGS="-Z sanitizer=leak" cargo run --target x86_64-unknown-linux-gnu; echo $?
    Finished dev [optimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/leak`

=================================================================
==10848==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 16 byte(s) in 1 object(s) allocated from:
    #0 0x557c3488db1f in __interceptor_malloc /shared/rust/checkouts/lsan/src/compiler-rt/lib/lsan/lsan_interceptors.cc:55
    #1 0x557c34888aaa in alloc::heap::exchange_malloc::h68f3f8b376a0da42 /shared/rust/checkouts/lsan/src/liballoc/heap.rs:138
    #2 0x557c34888afc in leak::main::hc56ab767de6d653a $PWD/src/main.rs:4
    #3 0x557c348c0806 in __rust_maybe_catch_panic ($PWD/target/debug/leak+0x3d806)

SUMMARY: LeakSanitizer: 16 byte(s) leaked in 1 allocation(s).
23
```

```
$ cargo new --bin racy && cd $_

$ edit src/main.rs && cat $_
```

``` rust
use std::thread;

static mut ANSWER: i32 = 0;

fn main() {
    let t1 = thread::spawn(|| unsafe { ANSWER = 42 });
    unsafe {
        ANSWER = 24;
    }
    t1.join().ok();
}
```

```
$ RUSTFLAGS="-Z sanitizer=thread" cargo run --target x86_64-unknown-linux-gnu; echo $?
==================
WARNING: ThreadSanitizer: data race (pid=12019)
  Write of size 4 at 0x562105989bb4 by thread T1:
    #0 racy::main::_$u7b$$u7b$closure$u7d$$u7d$::hbe13ea9e8ac73f7e $PWD/src/main.rs:6 (racy+0x000000010e3f)
    #1 _$LT$std..panic..AssertUnwindSafe$LT$F$GT$$u20$as$u20$core..ops..FnOnce$LT$$LP$$RP$$GT$$GT$::call_once::h2e466a92accacc78 /shared/rust/checkouts/lsan/src/libstd/panic.rs:296 (racy+0x000000010cc5)
    #2 std::panicking::try::do_call::h7f4d2b38069e4042 /shared/rust/checkouts/lsan/src/libstd/panicking.rs:460 (racy+0x00000000c8f2)
    #3 __rust_maybe_catch_panic <null> (racy+0x0000000b4e56)
    #4 std::panic::catch_unwind::h31ca45621ad66d5a /shared/rust/checkouts/lsan/src/libstd/panic.rs:361 (racy+0x00000000b517)
    #5 std::thread::Builder::spawn::_$u7b$$u7b$closure$u7d$$u7d$::hccfc37175dea0b01 /shared/rust/checkouts/lsan/src/libstd/thread/mod.rs:357 (racy+0x00000000c226)
    #6 _$LT$F$u20$as$u20$alloc..boxed..FnBox$LT$A$GT$$GT$::call_box::hd880bbf91561e033 /shared/rust/checkouts/lsan/src/liballoc/boxed.rs:605 (racy+0x00000000f27e)
    #7 std::sys::imp::thread::Thread::new::thread_start::hebdfc4b3d17afc85 <null> (racy+0x0000000abd40)

  Previous write of size 4 at 0x562105989bb4 by main thread:
    #0 racy::main::h23e6e5ca46d085c3 $PWD/src/main.rs:8 (racy+0x000000010d7c)
    #1 __rust_maybe_catch_panic <null> (racy+0x0000000b4e56)
    #2 __libc_start_main <null> (libc.so.6+0x000000020290)

  Location is global 'racy::ANSWER::h543d2b139f819b19' of size 4 at 0x562105989bb4 (racy+0x0000002f8bb4)

  Thread T1 (tid=12028, running) created by main thread at:
    #0 pthread_create /shared/rust/checkouts/lsan/src/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc:902 (racy+0x00000001aedb)
    #1 std::sys::imp::thread::Thread::new::hce44187bf4a36222 <null> (racy+0x0000000ab9ae)
    #2 std::thread::spawn::he382608373eb667e /shared/rust/checkouts/lsan/src/libstd/thread/mod.rs:412 (racy+0x00000000b5aa)
    #3 racy::main::h23e6e5ca46d085c3 $PWD/src/main.rs:6 (racy+0x000000010d5c)
    #4 __rust_maybe_catch_panic <null> (racy+0x0000000b4e56)
    #5 __libc_start_main <null> (libc.so.6+0x000000020290)

SUMMARY: ThreadSanitizer: data race $PWD/src/main.rs:6 in racy::main::_$u7b$$u7b$closure$u7d$$u7d$::hbe13ea9e8ac73f7e
==================
ThreadSanitizer: reported 1 warnings
66
```

```
$ cargo new --bin oob && cd $_

$ edit src/main.rs && cat $_
```

``` rust
fn main() {
    let xs = [0, 1, 2, 3];
    let y = unsafe { *xs.as_ptr().offset(4) };
}
```

```
$ RUSTFLAGS="-Z sanitizer=address" cargo run --target x86_64-unknown-linux-gnu; echo $?
=================================================================
==13328==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff29f3ecd0 at pc 0x55802dc6bf7e bp 0x7fff29f3ec90 sp 0x7fff29f3ec88
READ of size 4 at 0x7fff29f3ecd0 thread T0
    #0 0x55802dc6bf7d in oob::main::h0adc7b67e5feb2e7 $PWD/src/main.rs:3
    #1 0x55802dd60426 in __rust_maybe_catch_panic ($PWD/target/debug/oob+0xfe426)
    #2 0x55802dd58dd9 in std::rt::lang_start::hb2951fc8a59d62a7 ($PWD/target/debug/oob+0xf6dd9)
    #3 0x55802dc6c002 in main ($PWD/target/debug/oob+0xa002)
    #4 0x7fad8c3b3290 in __libc_start_main (/usr/lib/libc.so.6+0x20290)
    #5 0x55802dc6b719 in _start ($PWD/target/debug/oob+0x9719)

Address 0x7fff29f3ecd0 is located in stack of thread T0 at offset 48 in frame
    #0 0x55802dc6bd5f in oob::main::h0adc7b67e5feb2e7 $PWD/src/main.rs:1

  This frame has 1 object(s):
    [32, 48) 'xs' <== Memory access at offset 48 overflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow $PWD/src/main.rs:3 in oob::main::h0adc7b67e5feb2e7
Shadow bytes around the buggy address:
  0x1000653dfd40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000653dfd50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000653dfd60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000653dfd70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000653dfd80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x1000653dfd90: 00 00 00 00 f1 f1 f1 f1 00 00[f3]f3 00 00 00 00
  0x1000653dfda0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000653dfdb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000653dfdc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000653dfdd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000653dfde0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==13328==ABORTING
1
```

```
$ cargo new --bin uninit && cd $_

$ edit src/main.rs && cat $_
```

``` rust
use std::mem;

fn main() {
    let xs: [u8; 4] = unsafe { mem::uninitialized() };
    let y = xs[0] + xs[1];
}
```

```
$ RUSTFLAGS="-Z sanitizer=memory" cargo run; echo $?
==30198==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x563f4b6867da in uninit::main::hc2731cd4f2ed48f8 $PWD/src/main.rs:5
    #1 0x563f4b7033b6 in __rust_maybe_catch_panic ($PWD/target/debug/uninit+0x873b6)
    #2 0x563f4b6fbd69 in std::rt::lang_start::hb2951fc8a59d62a7 ($PWD/target/debug/uninit+0x7fd69)
    #3 0x563f4b6868a9 in main ($PWD/target/debug/uninit+0xa8a9)
    #4 0x7fe844354290 in __libc_start_main (/usr/lib/libc.so.6+0x20290)
    #5 0x563f4b6864f9 in _start ($PWD/target/debug/uninit+0xa4f9)

SUMMARY: MemorySanitizer: use-of-uninitialized-value $PWD/src/main.rs:5 in uninit::main::hc2731cd4f2ed48f8
Exiting
77
```