[Bug fortran/58001] New: Make it possible to silence "Extension: Tab character in format" warning

["burnus at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58001

            Bug ID: 58001
           Summary: Make it possible to silence "Extension: Tab character
                    in format" warning
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org

For indenting the source code, gfortran warns only with -std=f* or with -Wtab.

However, for format strings, it always warns - and with -std=f* it even turns
the warning into an error! (see io.c's next_char_not_space)

Example:

1894  format(   '123')
      end

(The tab is before '123'. A tab in the string itself is not warned for.)

Maybe the best would be to disable this warning with -std=legacy - and refer to
-std=legacy in the -std=gnu warning?