Test moves, items, and abilities in battle

Thank you to SBird for providing mgba-rom-test binaries and Spikes/Toxic
Spikes tests!

Co-authored-by: sbird <sbird@no.tld>

include/global.h

@@ -139,6 +139,14 @@
 #define NUM_FLAG_BYTES ROUND_BITS_TO_BYTES(FLAGS_COUNT)
 #define NUM_ADDITIONAL_PHRASE_BYTES ROUND_BITS_TO_BYTES(NUM_ADDITIONAL_PHRASES)
 
+// Calls m0/m1/.../m8 depending on how many arguments are passed.
+#define VARARG_8(m, ...) CAT(m, NARG_8(__VA_ARGS__))(__VA_ARGS__)
+#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];