[SYCL] Retain event in old OpenCL interop constructor

intel#6180 moved the retain logic for
events to the make_event interop API. However, this means that the old
OpenCL interop constructor for event does not retain the native event.
These changes add the retain logic directly to the old OpenCL interop
constructor for OpenCL.

Signed-off-by: Larsen, Steffen <steffen.larsen@intel.com>

Author: steffenlarsen

sycl/source/event.cpp

@@ -26,7 +26,12 @@ event::event() : impl(std::make_shared<detail::event_impl>()) {}
 
 event::event(cl_event ClEvent, const context &SyclContext)
     : impl(std::make_shared<detail::event_impl>(
-          detail::pi::cast<RT::PiEvent>(ClEvent), SyclContext)) {}
+          detail::pi::cast<RT::PiEvent>(ClEvent), SyclContext)) {
+  // This is a special interop constructor for OpenCL, so the event must be
+  // retained.
+  impl->getPlugin().call<detail::PiApiKind::piEventRetain>(
+      detail::pi::cast<RT::PiEvent>(ClEvent));
+}
 
 bool event::operator==(const event &rhs) const { return rhs.impl == impl; }