Pull Lexer's CharInfo table out for general use throughout Clang.

Rewriting the same predicates over and over again is bad for code size and
code maintainence. Using the functions in <ctype.h> is generally unsafe
unless they are specified to be locale-independent (i.e. only isdigit and
isxdigit).

The next commit will try to clean up uses of <ctype.h> functions within Clang.

llvm-svn: 174765