+is non-zero, then the function is variadic.
+.Pp
+Please note that if the compiler used to build the library does not support
+.Vt _Bool ,
+then
+.Vt cdecl_bool
+will be defined as
+.Vt signed char
+instead.
+In most cases these will have a compatible binary representation, provided
+that applications do not set
+.Va variadic
+to any values besides 0 or 1.