Update DefaultPluginScriptRunner.swift

Author: neonichu

Sources/Workspace/DefaultPluginScriptRunner.swift

@@ -119,6 +119,8 @@ public struct DefaultPluginScriptRunner: PluginScriptRunner, Cancellable {
 
         // We use the toolchain's Swift compiler for compiling the plugin.
         var commandLine = [self.toolchain.swiftCompilerPathForManifests.pathString]
+        
+        observabilityScope.emit(debug: "Using compiler \(self.toolchain.swiftCompilerPathForManifests.pathString)")
 
         // Get access to the path containing the PackagePlugin module and library.
         let pluginLibraryPath = self.toolchain.swiftPMLibrariesLocation.pluginLibraryPath