Excise <cctype> from Clang (except clang-tblgen) in favor of CharInfo.h.

Excise <cctype> from Clang (except clang-tblgen) in favor of CharInfo.h.

Nearly all of these changes are one-to-one replacements; the few that
aren't have to do with custom identifier validation.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174768 91177308-0d34-0410-b5e6-96231b3b80d8