Fix clang-tidy modernize-use-using warnings in headers

src/DNS_Mgr.h

@@ -16,7 +16,7 @@
 // These are defined in ares headers but we don't want to have to include
 // those headers here and create install dependencies on them.
 struct ares_channeldata;
-typedef struct ares_channeldata* ares_channel;
+using ares_channel = struct ares_channeldata*;
 #ifndef T_PTR
 #define T_PTR 12
 #endif

src/DebugCmds.h

@@ -68,6 +68,7 @@ int find_all_matching_cmds(const std::string& prefix, const char* array_of_match
 // These functions return <= 0 if failure, > 0 for success.
 // More particular return values are command-specific: see comments w/function.
 
+// NOLINTNEXTLINE(modernize-use-using)
 typedef int DbgCmdFn(DebugCmd cmd, const std::vector<std::string>& args);
 
 DbgCmdFn dbg_cmd_backtrace;