refactor: move some anonymous enums back to non-defs headers (#26622)

It isn't really useful to put anonymous enums only used as arguments to
functions calls in _defs.h headers, as they will only be used by a file
that calls those functions, which requires including a non-defs header.

Also move os_msg() and os_errmsg() back to message.h, as on Windows they
are actual functions instead of macros.

Also remove gettext.h and globals.h from private/helpers.h.

src/clint.py

@@ -905,7 +905,6 @@ def CheckIncludes(filename, lines, error):
             "src/nvim/buffer.h",
             "src/nvim/buffer_defs.h",
             "src/nvim/channel.h",
-            "src/nvim/channel_defs.h",
             "src/nvim/charset.h",
             "src/nvim/drawline.h",
             "src/nvim/eval.h",
@@ -950,8 +949,6 @@ def CheckIncludes(filename, lines, error):
             "klib/klist.h",
             "klib/kvec.h",
             "nvim/func_attr.h",
-            "nvim/gettext.h",
-            "nvim/globals.h"
             ]
 
     for i in check_includes_ignore: