[CMake] llvm-as depends on intrinsics_gen

llvm-as.cpp has the following include chain:

llvm/Bitcode/BitcodeWriter.h
llvm/IR/ModuleSummaryIndex.h
llvm/IR/Module.h
llvm/IR/Function.h
llvm/IR/Argument.h
llvm/IR/Attributes.h
llvm/IR/Attributes.gen

This means llvm-as needs to depend on intrinsics_gen.

llvm-svn: 287423