[test] Add missing memmove definition for wasm tests

7ae20b7 added a memmove dependency
to the embedded build, so we need to add a definition for it in the
test to satisfy the linker.

Author: kateinoigakukun

test/embedded/wasm/classes.swift

@@ -15,6 +15,9 @@
 
 int putchar(int c) { return c; }
 void free(void *ptr) {}
+void *memmove(void *dest, const void *src, size_t n) {
+    return __builtin_memmove(dest, src, n);
+}
 
 int posix_memalign(void **memptr, size_t alignment, size_t size) {
     uintptr_t mem = __builtin_wasm_memory_grow(0, (size + 0xffff) / 0x10000);