Move 'likely' macros to the compiler support header

This makes it easier to move away from autoconfig in the future.

Also, use '!!' C trick to prevent accidental incorrect usage of
these macros.

include/dosbox.h

@@ -21,6 +21,7 @@
 #define DOSBOX_DOSBOX_H
 
 #include "config.h"
+#include "compiler.h"
 #include "types.h"
 
 GCC_ATTRIBUTE(noreturn) void E_Exit(const char * message,...) GCC_ATTRIBUTE( __format__(__printf__, 1, 2));