PATCH: Add --alt-nops=short|long to x86/x86-64 assemblers

[Paul Brook]

> > Maybe I should add -march= and -mtune= to assembler.
>
> It sounds like it would be a good idea, although if it is only to
> support this new feature then you may not want to go that far.

FWIW I've found it more useful to add .cpu and/or .arch assembly directives. 
Handling the gcc spec strings for commandline controls and making sure the 
gcc and gas defaults are consistent can get painful, especially if gcc has 
several different ways of specifying the cpu variant.

Paul