Declarations for 2- and 3-argument GetMonData (#1756)

* Type-safe GetMonData/GetBoxMonData

* Comments

include/global.h

@@ -134,6 +134,13 @@
 #define NUM_FLAG_BYTES ROUND_BITS_TO_BYTES(FLAGS_COUNT)
 #define NUM_TRENDY_SAYING_BYTES ROUND_BITS_TO_BYTES(NUM_TRENDY_SAYINGS)
 
+// This returns the number of arguments passed to it (up to 8).
+#define NARG_8(...) NARG_8_(_, ##__VA_ARGS__, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+#define NARG_8_(_, a, b, c, d, e, f, g, h, N, ...) N
+
+#define CAT(a, b) CAT_(a, b)
+#define CAT_(a, b) a ## b
+
 // This produces an error at compile-time if expr is zero.
 // It looks like file.c:line: size of array `id' is negative
 #define STATIC_ASSERT(expr, id) typedef char id[(expr) ? 1 : -1];