Auto merge of rust-lang#140064 - EnzymeAD:enable-autodiff-in-ci, r=<try>

[DO NOT MERGE] start building enzyme on x86_64-gnu-llvm-{19|20} builders

My goal is to put this in CI on April 26, to have a week to land some of the outstanding PRs:
rust-lang#139700
rust-lang#139308
rust-lang#139557
rust-lang#140030
rust-lang#140049
The autodiff flags PR should land first, but otherwise they don't overlap and are mostly ready, so it shouldn't be too hard to land them. In the meantime, I'll experiment here with some builders.

r? `@oli-obk`

Tracking:

- rust-lang#124509

try-job: x86_64-gnu-llvm-19
try-job: x86_64-gnu-llvm-20

Author: bors

src/ci/docker/host-x86_64/x86_64-gnu-llvm-19/Dockerfile

@@ -52,6 +52,7 @@ ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \
       --llvm-root=/usr/lib/llvm-19 \
       --enable-llvm-link-shared \
+      --enable-llvm-enzyme \
       --set rust.randomize-layout=true \
       --set rust.thin-lto-import-instr-limit=10
 

src/ci/docker/host-x86_64/x86_64-gnu-llvm-20/Dockerfile

@@ -52,6 +52,7 @@ ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \
       --llvm-root=/usr/lib/llvm-20 \
       --enable-llvm-link-shared \
+      --enable-llvm-enzyme \
       --set rust.randomize-layout=true \
       --set rust.thin-lto-import-instr-limit=10