Fix Clang compilation with gig

src/core/MicroTimer.cpp

@@ -0,0 +1,27 @@
+#include "MicroTimer.h"
+
+using namespace std;
+using namespace std::chrono;
+
+static_assert(ratio_less_equal<steady_clock::duration::period, micro>::value, 
+	"MicroTimer: steady_clock doesn't support microsecond resolution");
+
+MicroTimer::MicroTimer()
+{
+	reset();
+}
+
+MicroTimer::~MicroTimer()
+{
+}
+
+void MicroTimer::reset()
+{
+	begin = steady_clock::now();
+}
+
+int MicroTimer::elapsed() const
+{
+	auto now = steady_clock::now();
+	return std::chrono::duration_cast<std::chrono::duration<int, std::micro>>(now - begin).count();
+}