[Bug libstdc++/104883] <system_error> should define all std::errc enumerators

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104883

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-09-22
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Created attachment 53613
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53613&action=edit
Generate error_constants.h from <errno.h>

    Instead of having several very similar target-specific headers with
    slightly different sets of enumerators, generate the error_constants.h
    file as part of the build. This ensures that all enumerators are always
    defined, with the value from the corresponding errno macro if present,
    or a libstdc++-specific alternative value.

    The libstdc++-specific values will be values greater than the positive
    integer _GLIBCXX_ERRC_ORIGIN, which defaults to 9999 but can be set in
    os_defines.h if a more suitable value exists for the OS (e.g. ELAST
    could be used for BSD targets).


The advantage of doing this is that we get a header that can be used
freestanding, but with values that match the hosted errno.h (if one exists on
the target).