Fix type comparison for C++20

The two are effectively different types and there is nothing which allows
implicitly casting between them. Also add some protection making sure we notice
if we change one of the two sides inadvertedly.

DataFormats/Headers/include/Headers/TimeStamp.h

@@ -138,12 +138,14 @@ class TimeStamp
     static_assert(std::is_same<typename T::rep, Rep>::value && std::is_same<typename T::period, Period>::value,
                   "only clock and duration types defining the rep and period member types are allowed");
     using duration = std::chrono::duration<Rep, Period>;
-    if (mUnit == sClockLHC) {
+    static_assert(sizeof(mUnit) == sizeof(sClockLHC), "size mismatch of mUnit and sClockLHC");
+    if (memcmp(&mUnit, &sClockLHC, sizeof(sClockLHC)) == 0) {
       // cast each part individually, if the precision of the return type
       // is smaller the values are simply truncated
       return std::chrono::duration_cast<duration>(LHCOrbitClock::duration(mPeriod) + LHCBunchClock::duration(mBCNumber));
     }
-    if (mUnit == sMicroSeconds) {
+    static_assert(sizeof(mUnit) == sizeof(sMicroSeconds), "size mismatch of mUnit and sMicroSeconds");
+    if (memcmp(&mUnit, &sMicroSeconds, sizeof(sMicroSeconds)) == 0) {
       // TODO: is there a better way to mark the subticks invalid for the
       // micro seconds representation? First step is probably to remove/rename the
       // variable