swift234

[Function Attribute] add target-cpu and target-features sets if they're non-null.

All llvm::Functions created during IRGen will have target-cpu and target-features
attributes if they are non-null.

Update testing cases to expect the attribute in function definition.
Add testing case function-target-features.swift to verify target-cpu and
target-features.

rdar://20772331


Swift SVN r28186