Fix the building error in android_deploy (#1262)

* Fix a link in android_deploy/README.md and a error while building android_deploy.

* revert and change APP_STL in Application.mk

apps/android_deploy/README.md

@@ -99,7 +99,7 @@ If everything goes well, you will find compile tools in `/opt/android-toolchain-
 
 ### Place compiled model on Android application assets folder
 
-Follow instruction to get compiled version model for android target [here.](https://tvm.ai/deploy/android.html)
+Follow instruction to get compiled version model for android target [here.](http://docs.tvm.ai/deploy/android.html)
 
 Copied these compiled model deploy_lib.so, deploy_graph.json and deploy_param.params to apps/android_deploy/app/src/main/assets/ and modify TVM flavor changes on [java](https://github.com/dmlc/tvm/blob/master/apps/android_deploy/app/src/main/java/ml/dmlc/tvm/android/demo/MainActivity.java#L81)
 

apps/android_deploy/app/src/main/jni/Application.mk

@@ -8,7 +8,7 @@ endif
 
 include $(config)
 
-APP_STL := gnustl_static
+APP_STL := c++_static
 
 APP_CPPFLAGS += -DDMLC_LOG_STACK_TRACE=0 -DTVM4J_ANDROID=1 -std=c++11 -Oz -frtti
 ifeq ($(USE_OPENCL), 1)                                                                                                                                             

src/runtime/thread_pool.cc

@@ -69,6 +69,8 @@ class ParallelLauncher {
       tvm::runtime::threading::Yield();
     }
     if (!has_error_.load()) return 0;
+    // the following is intended to use string due to
+    // security issue raised in SGX backend
     std::string err("");
     for (size_t i = 0; i < par_errors_.size(); ++i) {
       if (par_errors_[i].length() != 0) {