Auto merge of #53384 - gootorov:use-servo-smallvec, r=michaelwoerister

Use optimized SmallVec implementation

This PR replaces current SmallVec implementation with the one from the Servo project.

Closes https://github.com/rust-lang/rust/issues/51640

r? @Mark-Simulacrum

diff --cc src/librustc/hir/lowering.rs
Simple merge

diff --cc src/librustc/lib.rs
Simple merge

diff --cc src/librustc_mir/lib.rs
index 6a8157df0ccff03cd6e93029e5b7e80f857366d4,d36dbaa0608265425768bf35037f9f8370ff316f..617efed31d913f73c4e81653a134eb0307ef62fd
--- 1/src/librustc_mir/lib.rs
--- 2/src/librustc_mir/lib.rs
+++ b/src/librustc_mir/lib.rs
@@@ -61,15 -62,8 +61,16 @@@ extern crate log_settings
  extern crate rustc_apfloat;
  extern crate byteorder;
  extern crate core;
+ extern crate smallvec;
  
 +// Once we can use edition 2018 in the compiler,
 +// replace this with real try blocks.
 +macro_rules! try_block {
 +    ($($inside:tt)*) => (
 +        (||{ ::std::ops::Try::from_ok({ $($inside)* }) })()
 +    )
 +}
 +
  mod diagnostics;
  
  mod borrow_check;

diff --cc src/librustc_resolve/macros.rs
Simple merge

diff --cc src/libsyntax/ext/expand.rs
Simple merge

diff --cc src/libsyntax/fold.rs
Simple merge

diff --cc src/libsyntax/lib.rs
Simple merge