Merge pull request swiftlang#33950 from gottesmm/pr-4bccd8250f399d6de00468d798d40b170fe4edf2

[build-script-impl] Add a comment explaining why an option isn't truly dead as per reviewers suggestion.

Author: gottesmm

utils/build-script-impl

@@ -1797,6 +1797,12 @@ for host in "${ALL_HOSTS[@]}"; do
                     "${swift_cmake_options[@]}"
                 )
 
+                # NOTE: This is not a dead option! It is relied upon for certain
+                # bots/build-configs!
+                #
+                # TODO: In the future when we are always cross compiling and
+                # using Toolchain files, we should put this in either a
+                # toolchain file or a cmake cache.
                 if [[ "${BUILD_TOOLCHAIN_ONLY}" ]]; then
                     cmake_options+=(
                     -DSWIFT_TOOL_SIL_OPT_BUILD=FALSE