Reorder and shrink size of NameLen field in diagnostic group table. Shaves ~4K from clang binary.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189445 91177308-0d34-0410-b5e6-96231b3b80d8
Remove comment on the availability of boxed expressions.  They have been available for a while.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189446 91177308-0d34-0410-b5e6-96231b3b80d8