sprinkle LIKELY() on pp_hot.c scope.c and some *.h

sprinkle LIKELY() on pp_hot.c scope.c and some *.h

I've gone through pp_hot.c and scope.c and added LIKELY() or UNLIKELY()
to all conditionals where I understand the code well enough to know that
a particular branch is or isn't likely to be taken very often.

I also processed some of the .h files which contain commonly used macros.