STM32 driver: Space optimized SystemClock constructor

libuavcan_drivers/stm32/driver/include/uavcan_stm32/clock.hpp

@@ -59,8 +59,6 @@ class SystemClock : public uavcan::ISystemClock, uavcan::Noncopyable
 {
     SystemClock() { }
 
-    static SystemClock self;
-
     virtual uavcan::MonotonicTime getMonotonic()     const { return clock::getMonotonic(); }
     virtual uavcan::UtcTime getUtc()                 const { return clock::getUtc(); }
     virtual void adjustUtc(uavcan::UtcDuration adjustment) { clock::adjustUtc(adjustment); }

libuavcan_drivers/stm32/driver/src/uc_stm32_clock.cpp

@@ -217,16 +217,24 @@ uavcan::uint32_t getUtcAjdustmentJumpCount()
 
 } // namespace clock
 
-SystemClock SystemClock::self;
-
 SystemClock& SystemClock::instance()
 {
     MutexLocker mlocker(clock::mutex);
+
+    static union SystemClockStorage
+    {
+        uavcan::uint8_t buffer[sizeof(SystemClock)];
+        long long _aligner_1;
+        long double _aligner_2;
+    } storage;
+    SystemClock* const ptr = reinterpret_cast<SystemClock*>(storage.buffer);
+
     if (!clock::initialized)
     {
         clock::init();
+        new (ptr) SystemClock();
     }
-    return self;
+    return *ptr;
 }
 
 } // namespace uavcan_stm32