Move memory corruption tests up a directory

test/invalid_malloc_usable_size_small.c

@@ -0,0 +1,13 @@
+#include <malloc.h>
+
+#include "test_util.h"
+
+OPTNONE int main(void) {
+    char *p = malloc(16);
+    if (!p) {
+        return 1;
+    }
+    char *q = p + 4096 * 4;
+    malloc_usable_size(q);
+    return 0;
+}