[gamecode] Move pr_void_t to pr_comp.h

I think I had decided to put it there but forgot before committing the
size change, but I wound up needing it for qfcc.

include/QF/progs/pr_comp.h

@@ -534,6 +534,8 @@ typedef union pr_type_u {
 	pr_uint_t   uint_var;
 } pr_type_t;
 
+typedef pr_type_t pr_void_t;	// so size of void is 1
+
 typedef struct pr_va_list_s {
 	pr_int_t    count;
 	pr_ptr_t    list;			// pr_type_t

libs/gamecode/pr_opcode.c

@@ -33,8 +33,6 @@
 
 #include "QF/progs.h"
 
-typedef pr_type_t pr_void_t;	// so size of void is 1
-
 #define EV_TYPE(type) (sizeof (pr_##type##_t) / sizeof (pr_int_t)),
 VISIBLE const pr_ushort_t pr_type_size[ev_type_count] = {
 #include "QF/progs/pr_type_names.h"