Auto merge of #56678 - michaelwoerister:incr-thinlto-bench, r=<try>

[experiment] Benchmark incremental ThinLTO'd compiler.

I figure we can hijack perf.rlo to get some numbers on the runtime performance of code compiled with incremental ThinLTO. To this end, we compile the compiler incrementally and then measure how much slower it is a building stuff.

src/ci/docker/dist-x86_64-linux/Dockerfile

@@ -102,7 +102,8 @@ ENV RUST_CONFIGURE_ARGS \
       --set target.x86_64-unknown-linux-gnu.ar=/rustroot/bin/llvm-ar \
       --set target.x86_64-unknown-linux-gnu.ranlib=/rustroot/bin/llvm-ranlib \
       --set llvm.thin-lto=true \
-      --set rust.jemalloc
+      --set rust.jemalloc \
+      --set rust.incremental=true
 ENV SCRIPT python2.7 ../x.py dist --host $HOSTS --target $HOSTS
 ENV CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER=clang