autotools/siteinfo: Avoid races over siteinfo files
If a siteinfo enabled tasks re-executes at the wrong moment whilst something else is
in do_configure, the _config files can be removed which upsets autoconf and
causes build failures.
Use the same approach as we do for dealing with the aclocal files. We already
parse the manifests so look out any *_config files and if so, copy them, then
reference the copy from siteinfo instead. This has the advantage of also being
more deterministic.
[YOCTO #7101]
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
