[CMake] llvm-diff depends on intrinsics_gen

llvm-diff.cpp has the following include chain:

llvm/IR/Module.h
llvm/IR/Function.h
llvm/IR/Argument.h
llvm/IR/Attributes.h
llvm/IR/Attributes.gen

This means llvm-diff needs to depend on intrinsics_gen.

llvm-svn: 287427