CTest: adopt std::chrono::system_clock

After the refactor to make CTest use std::chrono::steady_clock for the
keeping of time for test duration, there are still references to
cmSystemTools::GetTime() left.
To further adopt std::chrono for time related activities, this commit
changes those remaining references to std::chrono::system_clock::now()
calls and alters the storage from either unsigned int or double to
std::chrono::system_clock::time_point.

For ease of conversion, a converter method is added to cmXMLWriter that
converts from a std::chrono::system_clock::time_point to the number of
seconds since the UN*X epoch as that is expected behaviour. This means
no more casts as required.

Functionally should be no difference as the system_clock is implemented
in the same terms.

1 files changed, 4 insertions, 5 deletions

diff --git a/Source/CTest/cmCTestBuildHandler.cxx b/Source/CTest/cmCTestBuildHandler.cxx
index 4ad4831..f25c9c3 100644
--- a/Source/CTest/cmCTestBuildHandler.cxx
+++ b/Source/CTest/cmCTestBuildHandler.cxx
@@ -407,7 +407,7 @@ int cmCTestBuildHandler::ProcessHandler()
 
   // Remember start build time
   this->StartBuild = this->CTest->CurrentTime();
-  this->StartBuildTime = cmSystemTools::GetTime();
+  this->StartBuildTime = std::chrono::system_clock::now();
   int retVal = 0;
   int res = cmsysProcess_State_Exited;
   if (!this->CTest->GetShowOnly()) {
@@ -421,7 +421,7 @@ int cmCTestBuildHandler::ProcessHandler()
 
   // Remember end build time and calculate elapsed time
   this->EndBuild = this->CTest->CurrentTime();
-  this->EndBuildTime = cmSystemTools::GetTime();
+  this->EndBuildTime = std::chrono::system_clock::now();
   auto elapsed_build_time =
     std::chrono::steady_clock::now() - elapsed_time_start;
 
@@ -488,8 +488,7 @@ void cmCTestBuildHandler::GenerateXMLHeader(cmXMLWriter& xml)
   this->CTest->GenerateSubprojectsOutput(xml);
   xml.StartElement("Build");
   xml.Element("StartDateTime", this->StartBuild);
-  xml.Element("StartBuildTime",
-              static_cast<unsigned int>(this->StartBuildTime));
+  xml.Element("StartBuildTime", this->StartBuildTime);
   xml.Element("BuildCommand", this->GetMakeCommand());
 }
 
@@ -644,7 +643,7 @@ void cmCTestBuildHandler::GenerateXMLFooter(
   xml.EndElement(); // Log
 
   xml.Element("EndDateTime", this->EndBuild);
-  xml.Element("EndBuildTime", static_cast<unsigned int>(this->EndBuildTime));
+  xml.Element("EndBuildTime", this->EndBuildTime);
   xml.Element(
     "ElapsedMinutes",
     std::chrono::duration_cast<std::chrono::minutes>(elapsed_build_time)