tradcpp: fix bool issue with newer compilers (GCC 15)

tradcpp/bool.h used the wrong check for determining C99+ stdbool.h
support by the compiler.  Use __STDC_VERSION__ rather than __STDC__.

cde/util/tradcpp/bool.h

@@ -30,7 +30,7 @@
 #ifndef BOOL_H
 #define BOOL_H
 
-#if __STDC__ > 199901
+#if __STDC_VERSION__ > 199901
 #include <stdbool.h>
 #else
 typedef int bool;