Add rand.h for non-qrand.c rand functions (#1684)

* sync rand.h with related oot PR

* fix

* yeet comment

src/code/sys_math.c

@@ -4,6 +4,7 @@
  */
 
 #include "global.h"
+#include "rand.h"
 
 static f32 sFactorialTbl[] = {
     1.0f, 1.0f, 2.0f, 6.0f, 24.0f, 120.0f, 720.0f, 5040.0f, 40320.0f, 362880.0f, 3628800.0f, 39916800.0f, 479001600.0f,

src/code/z_lib.c

@@ -3,6 +3,7 @@
 
 #include "libc64/qrand.h"
 
+#include "rand.h"
 #include "segmented_address.h"
 #include "sfx.h"
 #include "z64game.h"