The Android Open Source Project is licensed under the Apache License, Version 2.0 (the “License”) If you don’t need to do a full clean build but would like to touch some file or delete some intermediate files, add a clean step to the end of the list. These steps will only be run once, if they haven’t been run before. Newer CLEAN STEPS must be at the end OF THE LIST. Use “touch -c” and “rm -f” to gracefully deal with files that are missing or have been moved.”]
Source: https://android.googlesource.com/platform/libcore/+/android-cts-4.1_r4/CleanSpec.mk