*: add "noexcept" to many, many function prototypes

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

src/client/ClientMessage.hxx

@@ -53,6 +53,6 @@ public:
 
 gcc_pure
 bool
-client_message_valid_channel_name(const char *name);
+client_message_valid_channel_name(const char *name) noexcept;
 
 #endif