Now that predicates can be composed, simplify several of

the predicates by extending simple predicates to create
more complex predicates instead of duplicating the logic
for the simple predicates.

This doesn't reduce much redundancy in DAGISelEmitter.cpp's
generated source yet; that will require improvements to
DAGISelEmitter.cpp's instruction sorting, to make it more
effectively group nodes with similar predicates together.

llvm-svn: 57565