src: update cares_wrap OpenBSD defines

Move the `#define`s back into `cares_wrap.cc`, as they are part of
the implementation, not the declarations used in `cares_wrap.h`,
and apply the suggestion from
#38572 (comment)
to make the defines a bit more generic and not check for OpenBSD
specifically.

Refs: #38572

PR-URL: #38670
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: addaleax

Diff for: src/cares_wrap.cc

@@ -49,7 +49,11 @@
 # include <arpa/nameser.h>
 #endif
 
-#if defined(__OpenBSD__)
+// OpenBSD does not define these
+#ifndef AI_ALL
+# define AI_ALL 0
+#endif
+#ifndef AI_V4MAPPED
 # define AI_V4MAPPED 0
 #endif