[SYCL][PI] Equality operator for PI plugins

Implemented a comparison operator for the plugin class in SYCL RT:
Two plugins are equal if the pointer to their string is the same.

plugin constructor marked explicit to avoid accidental implicit
conversions.

Signed-off-by: Ruyman Reyes <[email protected]>

Author: Ruyman Reyes

sycl/source/detail/plugin.hpp

@@ -23,7 +23,7 @@ class plugin {
 public:
   plugin() = delete;
 
-  plugin(RT::PiPlugin Plugin) : MPlugin(Plugin) {
+  explicit plugin(RT::PiPlugin Plugin) : MPlugin(Plugin) {
     MPiEnableTrace = (std::getenv("SYCL_PI_TRACE") != nullptr);
   }
 
@@ -79,6 +79,17 @@ class plugin {
   bool MPiEnableTrace;
 
 }; // class plugin
+
+/// Two plugins are the same if their string is the same.
+/// There is no need to check the actual string, just the pointer, since
+/// there is only one instance of the PiPlugin struct per backend.
+///
+/// \ingroup sycl_pi
+///
+inline bool operator==(const plugin &lhs, const plugin &rhs) {
+  return (lhs.getPiPlugin().PluginVersion == rhs.getPiPlugin().PluginVersion);
+}
+
 } // namespace detail
 } // namespace sycl
 } // __SYCL_INLINE_NAMESPACE(cl)