[llvm][Support] Enable dl_iterate_phdr support on OpenBSD and DragonFly (llvm#125186)

Author: brad0

llvm/lib/Support/Unix/Signals.inc

@@ -468,7 +468,8 @@ void llvm::sys::AddSignalHandler(sys::SignalHandlerCallback FnPtr,
 
 #if ENABLE_BACKTRACES && defined(HAVE_BACKTRACE) &&                            \
     (defined(__linux__) || defined(__FreeBSD__) ||                             \
-     defined(__FreeBSD_kernel__) || defined(__NetBSD__))
+     defined(__FreeBSD_kernel__) || defined(__NetBSD__) ||                     \
+     defined(__OpenBSD__) || defined(__DragonFly__))
 struct DlIteratePhdrData {
   void **StackTrace;
   int depth;