libcpp: escape non-ASCII source bytes in -Wbidi-chars= [PR103026]

This flags rich_locations associated with -Wbidi-chars= so that
non-ASCII bytes will be escaped when printing the source lines
(using the diagnostics support I added in
r12-4825-gbd5e882cf6e0def3dd1bc106075d59a303fe0d1e).

In particular, this ensures that the printed source lines will
be pure ASCII, and thus the visual ordering of the characters
will be the same as the logical ordering.

Before:

  Wbidi-chars-1.c: In function ‘main’:
  Wbidi-chars-1.c:6:43: warning: unpaired UTF-8 bidirectional control character detected [-Wbidi-chars=]
      6 |     /*‮ } ⁦if (isAdmin)⁩ ⁦ begin admins only */
        |                                           ^
  Wbidi-chars-1.c:9:28: warning: unpaired UTF-8 bidirectional control character detected [-Wbidi-chars=]
      9 |     /* end admins only ‮ { ⁦*/
        |                            ^

  Wbidi-chars-11.c:6:15: warning: UTF-8 vs UCN mismatch when closing a context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
      6 | int LRE_‪_PDF_\u202c;
        |               ^
  Wbidi-chars-11.c:8:19: warning: UTF-8 vs UCN mismatch when closing a context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
      8 | int LRE_\u202a_PDF_‬_;
        |                   ^
  Wbidi-chars-11.c:10:28: warning: UTF-8 vs UCN mismatch when closing a context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
     10 | const char *s1 = "LRE_‪_PDF_\u202c";
        |                            ^
  Wbidi-chars-11.c:12:33: warning: UTF-8 vs UCN mismatch when closing a context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
     12 | const char *s2 = "LRE_\u202a_PDF_‬";
        |                                 ^

After:

  Wbidi-chars-1.c: In function ‘main’:
  Wbidi-chars-1.c:6:43: warning: unpaired UTF-8 bidirectional control character detected [-Wbidi-chars=]
      6 |     /*<U+202E> } <U+2066>if (isAdmin)<U+2069> <U+2066> begin admins only */
        |                                                                           ^
  Wbidi-chars-1.c:9:28: warning: unpaired UTF-8 bidirectional control character detected [-Wbidi-chars=]
      9 |     /* end admins only <U+202E> { <U+2066>*/
        |                                            ^

  Wbidi-chars-11.c:6:15: warning: UTF-8 vs UCN mismatch when closing a context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
      6 | int LRE_<U+202A>_PDF_\u202c;
        |                       ^
  Wbidi-chars-11.c:8:19: warning: UTF-8 vs UCN mismatch when closing a context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
      8 | int LRE_\u202a_PDF_<U+202C>_;
        |                   ^
  Wbidi-chars-11.c:10:28: warning: UTF-8 vs UCN mismatch when closing a context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
     10 | const char *s1 = "LRE_<U+202A>_PDF_\u202c";
        |                                    ^
  Wbidi-chars-11.c:12:33: warning: UTF-8 vs UCN mismatch when closing a context by "U+202C (POP DIRECTIONAL FORMATTING)" [-Wbidi-chars=]
     12 | const char *s2 = "LRE_\u202a_PDF_<U+202C>";
        |                                 ^

libcpp/ChangeLog:
	PR preprocessor/103026
	* lex.c (maybe_warn_bidi_on_close): Use a rich_location
	and call set_escape_on_output (true) on it.
	(maybe_warn_bidi_on_char): Likewise.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>