add -lzstd to ppx (facebook#534)

Summary:
fix link error on macos x86_64 noted in facebook#533. test results showing the fix works here:
https://github.com/shayne-fletcher/buck2/actions/runs/7515602243


Test Plan:
Imported from GitHub, without a `Test Plan:` line.
https://www.internalfb.com/sandcastle/workflow/4386506037060688764

Reviewed By: ndmitchell

Differential Revision: D52802355

Pulled By: shayne-fletcher

.circleci/config.yml

@@ -27,6 +27,7 @@ commands:
       - run:
           name: Set OCaml envs
           command: |
+            echo 'export PATH=/opt/homebrew/bin:"$PATH"' >> "$BASH_ENV"
             echo 'eval $(opam env)' >> "$BASH_ENV"
 
   setup_linux_env:
@@ -211,11 +212,12 @@ jobs:
       - run:
           name: Build example/prelude directory
           command: |
+            set -x
             cd examples/with_prelude
             /tmp/artifacts/buck2 init
             cp -r ../../prelude prelude
             # Additional setup for ocaml
-            source ./ocaml-setup.sh
+            ./ocaml-setup.sh
             /tmp/artifacts/buck2 build //... -v 2
             /tmp/artifacts/buck2 test //... -v 2
       - build_example_conan
@@ -252,7 +254,7 @@ jobs:
             /tmp/artifacts/buck2 init
             cp -r ../../prelude prelude
             # Additional setup for ocaml
-            source ./ocaml-setup.sh
+            ./ocaml-setup.sh
             /tmp/artifacts/buck2 build //... -v 2
             /tmp/artifacts/buck2 test //... -v 2
       - build_example_conan

examples/with_prelude/ocaml/ppx/BUCK

@@ -15,6 +15,8 @@ ocaml_binary(
     srcs = ["ppx_driver.ml"],
     compiler_flags = [
         "-linkall",
+        "-cclib",
+        "-lzstd",
     ],
     deps = [
         ":ppx-record-selectors",