fix emscripten dependencies by making separate test crate

lib/emscripten-tests/emtests/test_flexarray_struct.c

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2016 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+typedef struct {
+  uint16_t length;
+  struct {
+    int32_t int32;
+  } value[];
+} Tuple;
+
+int main() {
+  Tuple T[10];
+  Tuple *t = &T[0];
+
+  t->length = 4;
+  t->value->int32 = 100;
+
+  printf("(%d, %d)\n", t->length, t->value->int32);
+  return 0;
+}