autoconf 2.70 is coming soon which has some small behavioural fixes, so
backport a patch from upstream to fix the build with that release.
(From OE-Core rev: 954022e97c940239cee1789e4917e1c393dbf3fb)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>