Use wxGetUTCTimeUSec() in wxStopWatch under Unix for higher precision.

If gettimeofday() is available we can achieve better than millisecond
precision (even if it usually isn't as high as microsecond), so use it as
clock source in wxStopWatch.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69841 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/stopwatch.cpp

@@ -112,8 +112,15 @@ wxLongLong wxStopWatch::GetClockFreq() const
         return gs_perfCounter.freq.QuadPart;
 #endif // __WXMSW__
 
+#ifdef HAVE_GETTIMEOFDAY
+    // With gettimeofday() we can have nominally microsecond precision and
+    // while this is not the case in practice, it's still better than
+    // millisecond.
+    return MICROSECONDS_PER_SECOND;
+#else // !HAVE_GETTIMEOFDAY
     // Currently milliseconds are used everywhere else.
     return MILLISECONDS_PER_SECOND;
+#endif // HAVE_GETTIMEOFDAY/!HAVE_GETTIMEOFDAY
 }
 
 void wxStopWatch::Start(long t0)
@@ -134,7 +141,11 @@ wxLongLong wxStopWatch::GetCurrentClockValue() const
     }
 #endif // __WXMSW__
 
+#ifdef HAVE_GETTIMEOFDAY
+    return wxGetUTCTimeUSec();
+#else // !HAVE_GETTIMEOFDAY
     return wxGetUTCTimeMillis();
+#endif // HAVE_GETTIMEOFDAY/!HAVE_GETTIMEOFDAY
 }
 
 wxLongLong wxStopWatch::TimeInMicro() const