[mono][wasm] Fix a windows cross compiler issue. (#62339)

Fixes #61721.

Author: vargaz

src/mono/mono/mini/method-to-ir.c

@@ -2624,7 +2624,7 @@ emit_rgctx_fetch_inline (MonoCompile *cfg, MonoInst *rgctx, MonoJumpInfoRgctxEnt
 
 	int table_size = mono_class_rgctx_get_array_size (0, entry->in_mrgctx);
 	if (entry->in_mrgctx)
-		table_size -= MONO_SIZEOF_METHOD_RUNTIME_GENERIC_CONTEXT / sizeof (TARGET_SIZEOF_VOID_P);
+		table_size -= MONO_SIZEOF_METHOD_RUNTIME_GENERIC_CONTEXT / TARGET_SIZEOF_VOID_P;
 	MONO_EMIT_NEW_BIALU_IMM (cfg, OP_COMPARE_IMM, -1, slot_ins->dreg, table_size - 1);
 	MONO_EMIT_NEW_BRANCH_BLOCK (cfg, OP_PBGE, slowpath_bb);
 

src/mono/mono/mini/mini.h

@@ -1097,7 +1097,8 @@ typedef struct {
 	gpointer infos [MONO_ZERO_LEN_ARRAY];
 } MonoMethodRuntimeGenericContext;
 
-#define MONO_SIZEOF_METHOD_RUNTIME_GENERIC_CONTEXT (MONO_ABI_SIZEOF (MonoMethodRuntimeGenericContext) - MONO_ZERO_LEN_ARRAY * TARGET_SIZEOF_VOID_P)
+/* MONO_ABI_SIZEOF () would include the 'infos' field as well */
+#define MONO_SIZEOF_METHOD_RUNTIME_GENERIC_CONTEXT (TARGET_SIZEOF_VOID_P * 2)
 
 #define MONO_RGCTX_SLOT_MAKE_RGCTX(i)	(i)
 #define MONO_RGCTX_SLOT_MAKE_MRGCTX(i)	((i) | 0x80000000)