various build corrections

.github/workflows/core-build-nopch.yml

@@ -12,13 +12,6 @@ on:
       - synchronize
 
 concurrency:
-  # One concurrency group per workflow + ref.
-  #
-  # - PRs use `refs/pull/<PR_NUMBER>/merge`, so new commits cancel older
-  #   in-progress runs for the same PR.
-  # - When a PR is merged, a push to the target branch starts a new group,
-  #   canceling any still-running PR CI.
-  # - Branch pushes are isolated by ref.
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
@@ -53,4 +46,5 @@ jobs:
         with:
           CC: ${{ matrix.compiler.CC }}
           CXX: ${{ matrix.compiler.CXX }}
-          pch: false
+          pch: false
+          modules: true  # optional: include module compilation if desired