Avoid some warnings from Clang during the Android build.

src/client.cpp

@@ -1539,7 +1539,6 @@ public:
                 &jobs,
                 name_tag,
                 func = std::move(func),
-                exec,
                 job_type
             ] (Cancel& c, asio::yield_context y_) {
                 auto y = yield.detach(y_).tag(name_tag);

src/response_reader.h

@@ -65,7 +65,7 @@ slurp_response( AbstractReader& reader, size_t max_body_size
         if (part->is_trailer()) break;  // end of response
         if (!part->is_body() && !part->is_chunk_body()) continue;
 
-        const Body::Base* data;
+        const Body::Base* data = nullptr;
         if (auto b = part->as_body()) data = b;
         else if (auto cb = part->as_chunk_body()) data = cb;
         assert(data);

src/util/async_queue_reader.h

@@ -14,7 +14,7 @@ public:
         : _queue(q)
     {}
 
-    boost::optional<Part> async_read_part(Cancel cancel, asio::yield_context yield) {
+    boost::optional<Part> async_read_part(Cancel cancel, asio::yield_context yield) override {
         if (_cancel) return boost::none;
         auto c = _cancel.connect([&] { cancel(); });
         sys::error_code ec;
@@ -30,7 +30,7 @@ public:
         _queue.push_back(std::move(p));
     }
 
-    void close() {
+    void close() override {
         _queue.push_back(boost::none);
         _cancel();
     }