Explain rationale behind this change

Author: edymtt

utils/build-script-impl

@@ -542,9 +542,13 @@ function set_build_options_for_host() {
             esac
 
             if [[ "${DARWIN_SDK_DEPLOYMENT_TARGETS}" != "" ]]; then
+                # IFS is immediately unset after its use to avoid unwanted
+                # replacement of characters in subsequent lines.
                 local IFS=";"; DARWIN_SDK_DEPLOYMENT_TARGETS=($DARWIN_SDK_DEPLOYMENT_TARGETS); unset IFS
 
                 for target in "${DARWIN_SDK_DEPLOYMENT_TARGETS[@]}"; do
+                    # IFS is immediately unset after its use to avoid unwanted
+                    # replacement of characters in subsequent lines.
                     local IFS="-"; triple=($target); unset IFS
                     sdk_target=$(toupper ${triple[0]}_${triple[1]})
                     swift_cmake_options+=(