Comment on why we need to drop some messages produced by GHC.

haskell/private/ghc_wrapper.sh

@@ -12,6 +12,14 @@ if [ "$2" == "--persistent_worker" ]; then
     # wrapping GHC. Not ready for production usage.
     exec "${compile_flags[@]}" --persistent_worker
 else
+    # Drop messages that GHC produces on features that we rely upon.
+    #
+    # "Loaded" is emitted when using GHC environment files, which we
+    # use as poor man's response files for GHC.
+    #
+    # "Warning: the following files ..." is produced when we tell GHC
+    # to load object files in the interpreter in the build action
+    # of haskell_module which doesn't do any linking.
     while IFS= read -r line; do extra_args+=("$line"); done < "$2"
     "${compile_flags[@]}" "${extra_args[@]}" 2>&1 \
       | while IFS= read -r line; do [[ $line =~ ^(Loaded|Warning: the following files would be used as linker inputs, but linking is not being done:) ]] || echo "$line"; done >&2