perlPackages.YAMLSyck: fix build with gcc15

- add "-std=gnu17" to `env.NIX_CFLAGS_COMPILE`

Upstream issue:
https://www.github.com/cpan-authors/YAML-Syck/issues/61

There is a PR with proposed patch:
https://www.github.com/cpan-authors/YAML-Syck/pull/64
alpine uses it:
https://gitlab.alpinelinux.org/alpine/aports/-/commit/7dab2a77194967a52df82378c817f686d32056a7

Other distros settled on "-std=gnu17":
https://gitlab.archlinux.org/archlinux/packaging/packages/perl-yaml-syck/-/commit/9355df2bddfdda80963a629d750d0dbc1c1d8aa8
https://src.fedoraproject.org/rpms/perl-YAML-Syck/c/5fb93f7185d99ad738c985a944191ceb89368a82

Fixes build failure with gcc15:
```
emitter.c:161:9: error: too many arguments to function 'st_foreach';
expected 0, have 3
  161 |         st_foreach( e->anchors, syck_st_free_anchors, 0 );
      |         ^~~~~~~~~~  ~~~~~~~~~~
In file included from syck.h:36,
                 from emitter.c:15:
syck_st.h:35:6: note: declared here
   35 | void st_foreach(), st_add_direct(), st_free_table(), st_cleanup_safe();
      |      ^~~~~~~~~~
emitter.c:162:9: error: too many arguments to function 'st_free_table';
expected 0, have 1
  162 |         st_free_table( e->anchors );
      |         ^~~~~~~~~~~~~  ~~~~~~~~~~
syck_st.h:35:37: note: declared here
   35 | void st_foreach(), st_add_direct(), st_free_table(), st_cleanup_safe();
      |                                     ^~~~~~~~~~~~~
emitter.c:400:9: error: too many arguments to function 'st_lookup';
expected 0, have 3
  400 |         st_lookup( e->markers, n, (st_data_t *)&oid ) &&
      |         ^~~~~~~~~  ~~~~~~~~~~
syck_st.h:34:18: note: declared here
   34 | int st_insert(), st_lookup();
      |                  ^~~~~~~~~
```

Author: ghpzin

pkgs/top-level/perl-packages.nix

@@ -39082,6 +39082,7 @@ with self;
       url = "mirror://cpan/authors/id/T/TO/TODDR/YAML-Syck-1.34.tar.gz";
       hash = "sha256-zJFWzK69p5jr/i8xthnoBld/hg7RcEJi8X/608bjQVk=";
     };
+    env.NIX_CFLAGS_COMPILE = "-std=gnu17";
     meta = {
       description = "Fast, lightweight YAML loader and dumper";
       homepage = "https://github.com/toddr/YAML-Syck";