Performance improvements for System::getProcessTime (now ~30% faster)

• Increase test coverage and add performance check to test_GaudiTiming
• Remove unnecessary calls to getpid (saves ~10ns per query() call):
  • Remove getpid calls in case pid is -1 (self)
  • Remove ugly define that was hiding the getpid() calls in the source code
• Switch from getrusage() to times() (saves ~100ns per call)
• Only create ProcessHandle for Windows
• Add templated version of currentTime() so it can be inlined
• Allow System::getProcess to be inlined (move Windows code to constructor)
• Remove private caches for query() calls as those were not used

Milestone changed to %v28r0

Reassigned to @clemenci

Approved this merge request

Status changed to merged

mentioned in commit f4ae6f72

mentioned in merge request atlas/Gaudi!99 (merged)

mentioned in commit atlas/Gaudi@d710ddcd

mentioned in commit atlas/Gaudi@1a46d24c

Mentioned in commit ishapova/Gaudi@f4ae6f72