Auto merge of rust-lang#103591 - lqd:win-lto, r=Mark-Simulacrum

Enable ThinLTO for rustc on x64 msvc

This applies the great work from `@bjorn3` and `@Kobzol` in rust-lang#101403 to x64 msvc.

Here are the local results for the try build `68c5c85ed759334a11f0b0e586f5032a23f85ce4`, compared to its parent `0a6b941df354c59b546ec4c0d27f2b9b0cb1162c`. Looking better than my previous local builds.

![image](https://user-images.githubusercontent.com/247183/198158039-98ebac0e-da0e-462e-8162-95e88345edb9.png)

(I can't show cycle counts, as that option is failing on the windows version of the perf collector, but I'll try to analyze and debug this soon)

This will be the first of a few tests for rustc / llvm / both ThinLTO on the windows and mac targets.

.github/workflows/ci.yml

@@ -430,7 +430,7 @@ jobs:
             os: windows-latest-xl
           - name: dist-x86_64-msvc
             env:
-              RUST_CONFIGURE_ARGS: "--build=x86_64-pc-windows-msvc --host=x86_64-pc-windows-msvc --target=x86_64-pc-windows-msvc --enable-full-tools --enable-profiler"
+              RUST_CONFIGURE_ARGS: "--build=x86_64-pc-windows-msvc --host=x86_64-pc-windows-msvc --target=x86_64-pc-windows-msvc --enable-full-tools --enable-profiler --set rust.lto=thin"
               SCRIPT: PGO_HOST=x86_64-pc-windows-msvc src/ci/pgo.sh python x.py dist bootstrap --include-default-paths
               DIST_REQUIRE_ALL_TOOLS: 1
             os: windows-latest-xl

src/ci/github-actions/ci.yml

@@ -667,6 +667,7 @@ jobs:
                 --target=x86_64-pc-windows-msvc
                 --enable-full-tools
                 --enable-profiler
+                --set rust.lto=thin
               SCRIPT: PGO_HOST=x86_64-pc-windows-msvc src/ci/pgo.sh python x.py dist bootstrap --include-default-paths
               DIST_REQUIRE_ALL_TOOLS: 1
             <<: *job-windows-xl