Adds multibyte awareness to pretty-print.c

2019-12-11  Lewis Hyatt  <lhyatt@gmail.com>

	PR 91853
	* pretty-print.c (pp_quoted_string): Avoid hex-escaping valid
	multibyte input.  Fix off-by-one-bug printing the last byte before a
	hex-escaped output.
	(pp_character): Don't apply line wrapping in the middle of multibyte
	characters.
	(test_utf8): New test.
	(pretty_print_c_tests): Call the new test.

From-SVN: r279226