If dyld-info is not available, don't try to compile unreachable code
using it either.

--- gdb-1518/src/gdb/macosx/macosx-nat-dyld.c
+++ gdb-1518/src/gdb/macosx/macosx-nat-dyld.c
@@ -779,7 +779,7 @@
     {
 #if !defined (TASK_DYLD_INFO)
       return 0;
-#endif
+#else
       if (macosx_status->task == TASK_NULL)
         return 0;
 
@@ -799,6 +799,7 @@
           task_dyld_info.all_image_info_size == 0)
           return 0;
       s->dyld_image_infos = task_dyld_info.all_image_info_addr;
+#endif /* TASK_DYLD_INFO */
     }
 #endif /* NM_NEXTSTEP */