Sort all of Clang's files under 'lib', and fix up the broken headers

uncovered.

This required manually correcting all of the incorrect main-module
headers I could find, and running the new llvm/utils/sort_includes.py
script over the files.

I also manually added quite a few missing headers that were uncovered by
shuffling the order or moving headers up to be main-module-headers.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169237 91177308-0d34-0410-b5e6-96231b3b80d8