This change adds SMAC (signed multiply-accumulate) and UMAC (unsigned multiply-accumulate) for LEON subtargets of the Sparc processor.
The new files LeonFeatures.td and leon-instructions.ll will both be expanded in future, so I want to leave them separate as small files for this review, to be expanded in future check-ins.
Note: The functions are provided only for inline-assembly provision. No DAG selection is provided as this is not yet required by our project. If anyone knows the correct DAG matching rules, I'd be glad to add them.