We need to ensure any aclocal-copy directory is removed before we s
earch for .m4 files, else the locations .m4 files are found from can
vary depending on whether its the first or second time we run configure.
Clearing any existing aclocal-copy directory before we start resolves
this issue and makes builds deterministic again.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
