Build the compiler with -Ctarget-cpu=x86-64-v4

[est31]

Sister PR of #79043 . Main difference is v4 instead of v2.

[rust-highfive]

r? @Mark-Simulacrum

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[rust-highfive]

⚠️ Warning ⚠️

• These commits modify submodules.

[est31]

Oh wait, v4 is not supported by the perf hardware: #79043 (comment)

[Mark-Simulacrum]

(There's also no need for a separate PR for this, you can just push to the v2 PR and we can enqueue another perf run there).

[est31]

@Mark-Simulacrum didn't know that works. Will do it in that PR then!

[rust-log-analyzer]

The job mingw-check of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[command]/usr/bin/git submodule foreach --recursive git config --local --name-only --get-regexp 'http\.https\:\/\/github\.com\/\.extraheader' && git config --local --unset-all 'http.https://github.com/.extraheader' || :
[command]/usr/bin/git config --local http.https://github.com/.extraheader AUTHORIZATION: basic ***
##[endgroup]
##[group]Fetching the repository
[command]/usr/bin/git -c protocol.version=2 fetch --no-tags --prune --progress --no-recurse-submodules --depth=2 origin +15b803db2a327add510127d2c3200aed0fc9cf01:refs/remotes/pull/79044/merge
---
configure: rust.channel         := nightly
configure: rust.debug-assertions := True
configure: llvm.assertions      := True
configure: dist.missing-tools   := True
configure: build.configure-args := ['--enable-sccache', '--disable-manage-submodu ...
configure: writing `config.toml` in current directory
configure: 
configure: run `python /checkout/x.py --help`
configure: 
---
skip untracked path cpu-usage.csv during rustfmt invocations
skip untracked path src/doc/book/ during rustfmt invocations
skip untracked path src/doc/rust-by-example/ during rustfmt invocations
skip untracked path src/llvm-project/ during rustfmt invocations
Diff in /checkout/src/bootstrap/compile.rs at line 522:
Running `"/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt" "--config-path" "/checkout" "--edition" "2018" "--unstable-features" "--skip-children" "--check" "/checkout/src/bootstrap/compile.rs"` failed.
 }
 
 
-pub fn rustc_cargo(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelection, compiler: Compiler) {
+pub fn rustc_cargo(
+    builder: &Builder<'_>,
If you're running `tidy`, try again with `--bless`. Or, if you just want to format code, run `./x.py fmt` instead.
+    cargo: &mut Cargo,
+    compiler: Compiler,
+) {
     cargo
     cargo
         .arg("--features")
         .arg(builder.rustc_features())
Diff in /checkout/src/bootstrap/compile.rs at line 531:
     rustc_cargo_env(builder, cargo, target, compiler);
 
 
-pub fn rustc_cargo_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelection, compiler: Compiler) {
+pub fn rustc_cargo_env(
+    builder: &Builder<'_>,
+    cargo: &mut Cargo,
+    compiler: Compiler,
+) {
+) {
     // Set some configuration variables picked up by build scripts and
     // the compiler alike
failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test --stage 2 src/tools/tidy
Build completed unsuccessfully in 0:00:20
== clock drift check ==
  local time: Sat Nov 14 15:44:20 UTC 2020

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