Isolated emscripten in new lib

lib/emscripten/emtests/test_alloca_stack.c

@@ -0,0 +1,23 @@
+/*
+ * 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.
+ */
+
+// We should not blow up the stack with numerous allocas
+#include <stdio.h>
+#include <stdlib.h>
+
+int func(int i) {
+  char *pc = (char *)alloca(100);
+  *pc = i;
+  (*pc)++;
+  return (*pc) % 10;
+}
+int main() {
+  int total = 0;
+  for (int i = 0; i < 1024 * 1024; i++) total += func(i);
+  printf("ok:%d*\n", total);
+  return 0;
+}