ram.ld must be rebuilt every time the configuration changes. It was
supposed to be like that, but it was not.

So, the older ram.ld was used when first building with a new config,
and only the second time the rule was used. This was exposed by
failuers in ./MAKEALL where each configuration is built only once.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>