meta: define _GNU_SOURCE to get strptime() from <time.h>

To use `strptime()`, the documentation indicates

  #define _XOPEN_SOURCE
  #include <time.h>

However, previously this was done wrongly.

For example, when building with musl we got a warning:

      CC       meta.lo
    meta.c:40: warning: "_XOPEN_SOURCE" redefined
       40 | #define _XOPEN_SOURCE
          |
    In file included from /usr/include/errno.h:8,
                     from meta.c:13:
    /usr/include/features.h:16: note: this is the location of the previous definition
       16 | #define _XOPEN_SOURCE 700
          |

Defining "__USE_XOPEN" is wrong. This is a glibc internal define not for
the user.

Note that if we just set _XOPEN_SOURCE (or _XOPEN_SOURCE=700), we won't
get other things like "struct tm.tm_gmtoff".

Instead, we already define _GNU_SOURCE at other places. Do that here
too, it will give us strptime() and all is good.

Also, those directives should be defined as first thing (or via "-D"
command line). See [1].

This is also important, because to use "time_t" in a header, we would
need to include <time.h>. That only works, if we get the feature test
macros right. That is, define the _?_SOURCE macro as first thing.

[1] https://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html

Signed-off-by: Thomas Haller <thaller@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

0 files changed, 0 insertions, 0 deletions