treewide: use boost::lround when std::round is unavailable

This is the case with uClibc-ng currently.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry picked from commit 769cd0ee9f0cf8ceb026aa751b5d4a390bb5dbdc)
(changed define to match master)

src/command/PlayerCommands.cxx

@@ -34,13 +34,12 @@
 #include "util/StringBuffer.hxx"
 #include "util/ScopeExit.hxx"
 #include "util/Exception.hxx"
+#include "util/Math.hxx"
 
 #ifdef ENABLE_DATABASE
 #include "db/update/Service.hxx"
 #endif
 
-#include <cmath>
-
 #define COMMAND_STATUS_STATE            "state"
 #define COMMAND_STATUS_REPEAT           "repeat"
 #define COMMAND_STATUS_SINGLE           "single"
@@ -154,7 +153,7 @@ handle_status(Client &client, gcc_unused Request args, Response &r)
 
 	if (pc.GetCrossFade() > FloatDuration::zero())
 		r.Format(COMMAND_STATUS_CROSSFADE ": %lu\n",
-			 std::lround(pc.GetCrossFade().count()));
+			 lround(pc.GetCrossFade().count()));
 
 	if (pc.GetMixRampDelay() > FloatDuration::zero())
 		r.Format(COMMAND_STATUS_MIXRAMPDELAY ": %f\n",