More N3077 raw string changes
* charset.c (cpp_interpret_string): Don't transform UCNs in raw
strings.
* lex.c (bufring_append): Split out from...
(lex_raw_string): ...here. Undo trigraph and line splicing
transformations. Do process line notes in multi-line literals.
(_cpp_process_line_notes): Ignore notes that were already handled.
From-SVN: r157804
