Fix FreeBSD build error in r287920

The conditional expression is ambiguous there, so help it by explicitly casting.
This will go away once we use chrono all the way down.

llvm-svn: 287921
diff --git a/lldb/source/Core/Communication.cpp b/lldb/source/Core/Communication.cpp
index 47616cc..c82e2fe 100644
--- a/lldb/source/Core/Communication.cpp
+++ b/lldb/source/Core/Communication.cpp
@@ -115,6 +115,8 @@
 size_t Communication::Read(void *dst, size_t dst_len,
                            const Timeout<std::micro> &timeout,
                            ConnectionStatus &status, Error *error_ptr) {
+  using std::chrono::microseconds;
+
   lldb_private::LogIfAnyCategoriesSet(
       LIBLLDB_LOG_COMMUNICATION,
       "%p Communication::Read (dst = %p, dst_len = %" PRIu64
@@ -141,8 +143,8 @@
     listener_sp->StartListeningForEvents(
         this, eBroadcastBitReadThreadGotBytes | eBroadcastBitReadThreadDidExit);
     EventSP event_sp;
-    std::chrono::microseconds listener_timeout =
-        timeout ? *timeout : std::chrono::microseconds(0);
+    microseconds listener_timeout =
+        timeout ? microseconds(*timeout) : microseconds(0);
     while (listener_sp->WaitForEvent(listener_timeout, event_sp)) {
       const uint32_t event_type = event_sp->GetType();
       if (event_type & eBroadcastBitReadThreadGotBytes) {