There is no reason to include ostream here, include iosfwd instead.

This file was schizophrenic when it came to representing sizes.  In some
cases it represented them as 'unsigneds', which are not enough for 64-bit
hosts.  In other cases, it represented them as uint64_t's, which are
inefficient for 32-bit hosts.

This patch unifies all of the sizes to use size_t instead.

llvm-svn: 19917