Recap and patch to deprecating cross-compiler stuff

[Bonzini]

Paul, 

thanks for the material about specifying the build type as an
option.  Indeed, that's what autoconf does, except that the
error message is wrong.

So this does not need to be deprecated and much less removed.
Here is an updated patch that removes the deprecation, but
still changes the other bits.

Paolo

ac-remove-xcompile-transition-2.patch
Description: Text document