Stub out a process creation time lookup for macOS.

We have an existing utility to look up the creation time of a process,
but the only implementation is for Linux. This has been fine so far, as
Launcher seems to be the only consumer of this API, but the compile-time
guard is now generating issues for us when trying to build that project
on macOS.

So this commit stubs out a macOS implementation that returns an error.
Ideally, we'd actually implement this for macOS, but doing so turns out
to be nontrivial [0] so I don't think it's worth pursing at this time.

[0]: https://stackoverflow.com/questions/31603885/get-process-creation-date-time-in-osx-with-c-c

Signed-off-by: Aaron Jacobs <[email protected]>

src/cpp/core/include/core/system/System.hpp

@@ -328,7 +328,7 @@ struct ProcessInfo
  std::string state;
  std::vector<std::string> arguments;
 
-#if !defined _WIN32 && !defined __APPLE__
+#ifndef _WIN32
  core::Error creationTime(boost::posix_time::ptime* pCreationTime) const;
 #endif
 };

src/cpp/core/system/PosixSystem.cpp

@@ -1955,6 +1955,11 @@ Error processInfo(const std::string& process, std::vector<ProcessInfo>* pInfo, b
 
  return Success();
 }
+
+Error ProcessInfo::creationTime(boost::posix_time::ptime* pCreationTime) const
+{
+ return systemError(boost::system::errc::not_supported, ERROR_LOCATION);
+}
 #endif
 
 std::ostream& operator<<(std::ostream& os, const ProcessInfo& info)