DATE are referenced by patch_do_patch
TIME are referenced by do_distro_check/do_checkpkg
BBPATH/THISDIR/_ impacts the scenario when using different source path.
DL_DIR/SSTATE_DIR are listed as dependency too, by pstaging_fetch
FILESEXTRPATHS is referenced by .bbappend files
Some tasks may not contribute to sstate packages, e.g. do_checkpkg. But for
safety all of them are whitelist this time.
