FunctionComparator attempts to produce a stable comparison of two Function
instances by looking at all available properties. Since ByVal attributes now
contain a Type pointer, they are not trivially ordered and FunctionComparator
should use its own Type comparison logic to sort them.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364523 91177308-0d34-0410-b5e6-96231b3b80d8