Enable -Wshorten-64-to-32 in wangle

Summary:
1. Add `"-Wshorten-64-to-32"` to `_extra_clang_flags`
2. Fix warnings generated from `buck build --keep-going wangle/...`

Reviewed By: chadaustin

Differential Revision: D19647345

fbshipit-source-id: 417840fe82ed3d5c9c2d989a0acf67e12758c1f9

folly/io/async/test/BlockingSocket.h

@@ -56,7 +56,8 @@ class BlockingSocket : public folly::AsyncSocket::ConnectCallback,
 
   void open(
       std::chrono::milliseconds timeout = std::chrono::milliseconds::zero()) {
-    sock_->connect(this, address_, timeout.count());
+    DCHECK_LE(timeout.count(), std::numeric_limits<int>::max());
+    sock_->connect(this, address_, folly::to_narrow(timeout.count()));
     eventBase_.loop();
     if (err_.hasValue()) {
       throw err_.value();
@@ -79,7 +80,7 @@ class BlockingSocket : public folly::AsyncSocket::ConnectCallback,
     if (err_.hasValue()) {
       throw err_.value();
     }
-    return len;
+    return folly::to_narrow(folly::to_signed(len));
   }
 
   void flush() {}
@@ -160,6 +161,6 @@ class BlockingSocket : public folly::AsyncSocket::ConnectCallback,
       throw folly::AsyncSocketException(
           folly::AsyncSocketException::UNKNOWN, "eof");
     }
-    return len - readLen_;
+    return folly::to_narrow(folly::to_signed(len - readLen_));
   }
 };