Refactor inlining decisions so that inexpensive criteria are considered first:

1. Based on code generation attributes.
2. Based on MIR availability (examines call graph).
3. Based on MIR body.

Fix rust-lang#82488

…tions

Signed-off-by: Nell Shamrell <nellshamrell@gmail.com>

For example, gdb:

```
(gdb) info threads
  Id   Target Id                                          Frame
  1    Thread 0x7fffefa7ec40 (LWP 2905) "rustc"           __pthread_clockjoin_ex (threadid=140737214134016, thread_return=0x0, clockid=<optimized out>, abstime=<optimized out>, block=<optimized out>)
    at pthread_join_common.c:145
  2    Thread 0x7fffefa7b700 (LWP 2957) "rustc"           0x00007ffff125eaa8 in llvm::X86_MC::initLLVMToSEHAndCVRegMapping(llvm::MCRegisterInfo*) ()
   from /home/wesley/.rustup/toolchains/stage1/lib/librustc_driver-f866439e29074957.so
  3    Thread 0x7fffeef0f700 (LWP 3116) "rustc"           futex_wait_cancelable (private=0, expected=0, futex_word=0x7fffe8602ac8) at ../sysdeps/nptl/futex-internal.h:183
* 4    Thread 0x7fffeed0e700 (LWP 3123) "rustc"           rustc_codegen_ssa::back::write::spawn_work (cgcx=..., work=...) at /home/wesley/code/rust/rust/compiler/rustc_codegen_ssa/src/back/write.rs:1573
  6    Thread 0x7fffe113b700 (LWP 3150) "opt foof.7rcbfp" 0x00007ffff2940e62 in llvm::CallGraph::populateCallGraphNode(llvm::CallGraphNode*) ()
   from /home/wesley/.rustup/toolchains/stage1/lib/librustc_driver-f866439e29074957.so
  8    Thread 0x7fffe0d39700 (LWP 3158) "opt foof.7rcbfp" 0x00007fffefe8998e in malloc_consolidate (av=av@entry=0x7ffe2c000020) at malloc.c:4492
  9    Thread 0x7fffe0f3a700 (LWP 3162) "opt foof.7rcbfp" 0x00007fffefef27c4 in __libc_open64 (file=0x7fffe0f38608 "foof.foof.7rcbfp3g-cgu.6.rcgu.o", oflag=524865) at ../sysdeps/unix/sysv/linux/open64.c:48
(gdb)
```

For browsers that support woff2 (most modern ones:
https://caniuse.com/woff2), this offers a reduction in download size
for these two fonts from 362k to 257k (32% reduction). It decreases the
total page size for `struct.String.html` (counting all subresources) by
about 2.5%.

If this is interesting, I'm happy to apply the same treatment to the
other fonts, but these two are the biggest.

…=m-ou-se

Stabilize str_split_once

Closes rust-lang#74773

…tebank

Reword labels on E0308 involving async fn return type

Fix for rust-lang#80658.

When someone writes code like this:

```rust
fn foo() -> u8 {
    async fn async_fn() -> () {}

    async_fn()
}
```

And they try to compile it, they will see an error that looks like this:

```bash
error[E0308]: mismatched types
 --> test.rs:4:5
  |
1 | fn foo() -> u8 {
  |             -- expected `u8` because of return type
2 |     async fn async_fn() -> () {}
  |                            -- checked the `Output` of this `async fn`, found opaque type
3 |
4 |     async_fn()
  |     ^^^^^^^^^^ expected `u8`, found opaque type
  |
  = note: while checking the return type of this `async fn`
  = note:     expected type `u8`
          found opaque type `impl Future`
```

Replaced some unwrap_or and map_or with lazy variants

Replaced some `unwrap_or` and `map_or` with `unwrap_or_else` and `map_or_else`.

Consider inexpensive inlining criteria first

Refactor inlining decisions so that inexpensive criteria are considered first:

1. Based on code generation attributes.
2. Based on MIR availability (examines call graph).
3. Based on MIR body.

Properly account for non-shorthand pattern field in unused variable lint

Fix rust-lang#82488

…s, r=nagisa

Set codegen thread names

Set names on threads spawned during codegen. Various debugging and profiling tools can take advantage of this to show a more useful identifier for threads.

For example, gdb will show thread names in `info threads`:

```
(gdb) info threads
  Id   Target Id                                          Frame
  1    Thread 0x7fffefa7ec40 (LWP 2905) "rustc"           __pthread_clockjoin_ex (threadid=140737214134016, thread_return=0x0, clockid=<optimized out>, abstime=<optimized out>, block=<optimized out>)
    at pthread_join_common.c:145
  2    Thread 0x7fffefa7b700 (LWP 2957) "rustc"           0x00007ffff125eaa8 in llvm::X86_MC::initLLVMToSEHAndCVRegMapping(llvm::MCRegisterInfo*) ()
   from /home/wesley/.rustup/toolchains/stage1/lib/librustc_driver-f866439e29074957.so
  3    Thread 0x7fffeef0f700 (LWP 3116) "rustc"           futex_wait_cancelable (private=0, expected=0, futex_word=0x7fffe8602ac8) at ../sysdeps/nptl/futex-internal.h:183
* 4    Thread 0x7fffeed0e700 (LWP 3123) "rustc"           rustc_codegen_ssa::back::write::spawn_work (cgcx=..., work=...) at /home/wesley/code/rust/rust/compiler/rustc_codegen_ssa/src/back/write.rs:1573
  6    Thread 0x7fffe113b700 (LWP 3150) "opt foof.7rcbfp" 0x00007ffff2940e62 in llvm::CallGraph::populateCallGraphNode(llvm::CallGraphNode*) ()
   from /home/wesley/.rustup/toolchains/stage1/lib/librustc_driver-f866439e29074957.so
  8    Thread 0x7fffe0d39700 (LWP 3158) "opt foof.7rcbfp" 0x00007fffefe8998e in malloc_consolidate (av=av@entry=0x7ffe2c000020) at malloc.c:4492
  9    Thread 0x7fffe0f3a700 (LWP 3162) "opt foof.7rcbfp" 0x00007fffefef27c4 in __libc_open64 (file=0x7fffe0f38608 "foof.foof.7rcbfp3g-cgu.6.rcgu.o", oflag=524865) at ../sysdeps/unix/sysv/linux/open64.c:48
(gdb)
```

and Windows Performance Analyzer will also show this information when profiling:

![image](https://user-images.githubusercontent.com/831192/109231017-d311f780-7793-11eb-8072-ab836a830e90.png)

rustdoc: add optional woff2 versions of FiraSans.

For browsers that support woff2 (most modern ones:
https://caniuse.com/woff2), this offers a reduction in download size
for these two fonts from 362k to 257k (32% reduction). It decreases the
total page size for `struct.String.html` (counting all subresources) by
about 2.5%.

If this is interesting, I'm happy to apply the same treatment to the
other fonts, but these two are the biggest.

…lize-css, r=apiraino

Revert "Update normalize.css to 8.0.1"

Reverts rust-lang#82313

Fixes rust-lang#82548
Fixes rust-lang#82542

``@jsha:`` I'm reverting until we can come up with a new version which is fully working.

r? ``@jyn514``