[Bug preprocessor/77810] New: provide format_inform_at_substring to go with format_warning_at_substring

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77810

            Bug ID: 77810
           Summary: provide format_inform_at_substring to go with
                    format_warning_at_substring
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The file substring-locations.h declares the function bool
format_warning_at_substring (const substring_loc&, const source_range*, const
char*, int, const char*, ...) to position the caret and underscores in warning
messages involving string literals.  It would be useful to also provide the
corresponding format_inform_at_substring and perhaps even
format_error_at_substring functions to make the same functionality available to
informational messages (and errors).