Implement C++0x user-defined string literals.

The extra data stored on user-defined literal Tokens is stored in extra
allocated memory, which is managed by the PreprocessorLexer because there isn't
a better place to put it that makes sure it gets deallocated, but only after
it's used up. My testing has shown no significant slowdown as a result, but
independent testing would be appreciated.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112458 91177308-0d34-0410-b5e6-96231b3b80d8
28 files changed