package/uhd: fix build with gcc 11

Fix the following build failure with gcc 11:

In file included from /tmp/instance-4/output-1/build/uhd-3.15.0.0/host/lib/usrp/dboard/e3xx/e3xx_ad9361_iface.hpp:14,
                 from /tmp/instance-4/output-1/build/uhd-3.15.0.0/host/lib/usrp/dboard/e3xx/e3xx_ad9361_iface.cpp:7:
/tmp/instance-4/output-1/build/uhd-3.15.0.0/host/lib/include/uhdlib/utils/rpc.hpp: In function 'bool {anonymous}::await_rpc_connected_state(std::shared_ptr<rpc::client>, std::chrono::milliseconds)':
/tmp/instance-4/output-1/build/uhd-3.15.0.0/host/lib/include/uhdlib/utils/rpc.hpp:28:27: error: 'sleep_for' is not a member of 'std::this_thread'
   28 |         std::this_thread::sleep_for(std::chrono::milliseconds(1));
      |                           ^~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/1591ff7fabb09e4eb79f3aa293fbb228c255c45b

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/uhd/0004-lib-Fix-missing-includes-in-rpc-hpp.patch

@@ -0,0 +1,28 @@
+From 9c4d9d826a6f40f199c526afd5ec168d5d088591 Mon Sep 17 00:00:00 2001
+From: Martin Braun <martin.braun@ettus.com>
+Date: Fri, 29 Jan 2021 12:23:50 +0100
+Subject: [PATCH] lib: Fix missing includes in rpc.hpp
+
+[Retrieved from:
+https://github.com/EttusResearch/uhd/commit/9c4d9d826a6f40f199c526afd5ec168d5d088591]
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+---
+ host/lib/include/uhdlib/utils/rpc.hpp | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/host/lib/include/uhdlib/utils/rpc.hpp b/host/lib/include/uhdlib/utils/rpc.hpp
+index e87a2ee324..ca89c10547 100644
+--- a/host/lib/include/uhdlib/utils/rpc.hpp
++++ b/host/lib/include/uhdlib/utils/rpc.hpp
+@@ -12,7 +12,11 @@
+ #include <rpc/client.h>
+ #include <rpc/rpc_error.h>
+ #include <boost/format.hpp>
++#include <chrono>
+ #include <memory>
++#include <mutex>
++#include <string>
++#include <thread>
+ 
+ namespace {
+