when build with EXTERNALSRC, checksum of EXTERNALSRC is one of inputs
for generate sigdata of task do_compile. without change any source, the
sigdata will not changed, and buildclean task only do make clean, and
not clean stampfiles like clean task, so the stampfile keep there, then
do_compile after do_buildclean will not rerun, and targetfile
tempdir_mdadm/mdadm will not be generated, report below error:
AssertionError: '/tmp/devtoolqarxv8ct6u/mdadm' does not exist
Fix by add a comments in Makefile to trigger rebuild of compile task
Signed-off-by: Changqing Li <changqing.li@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
