Fix clang cvar build

Add format(printf,...) annotation to varargs functions to move format
string checking up one level.

common/main/cmd.h

@@ -12,6 +12,7 @@
  */
 
 #pragma once
+#include "dxxsconf.h"
 
 void cmd_init(void);
 
@@ -22,6 +23,7 @@ void cmd_init(void);
 
 /* Add some commands to the queue to be executed */
 void cmd_enqueue(int insert, const char *input);
+__attribute_format_printf(2, 3)
 void cmd_enqueuef(int insert, const char *fmt, ...);
 #define cmd_append(input) cmd_enqueue(0, (input))
 #define cmd_appendf(...) cmd_enqueuef(0, __VA_ARGS__)

common/main/cvar.h

@@ -17,6 +17,7 @@
 #include <string>
 #include <physfs.h>
 #include "maths.h"
+#include "dxxsconf.h"
 
 // cvar flags
 #define CVAR_NONE           0
@@ -57,6 +58,7 @@ void cvar_registervariable (cvar_t &cvar);
 
 /* Set a CVar's value */
 void cvar_set_cvar(cvar_t *cvar, const char *value);
+__attribute_format_printf(2, 3)
 void cvar_set_cvarf(cvar_t *cvar, const char *fmt, ...);
 
 /* Equivalent to typing <var_name> <value> at the console */