Add a test for x86_64 in overrides where is was being incorrectly handled.
There was a previous fix (3a3be518536acc868c7eeb3c1111ad1b321480b7) but
this ensures we don't regress.
(Bitbake rev: 08c314eac231ac9292c8c95f1c5a6fc2023fe749)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>