add SystemInfo for libretro

BizHawk.Client.Common/Global.cs

@@ -145,6 +145,8 @@ namespace BizHawk.Client.Common
 						return SystemInfo.PSX;
 					case "AppleII":
 						return SystemInfo.AppleII;
+					case "Libretro":
+						return SystemInfo.Libretro;
 				}
 			}
 		}

BizHawk.Client.Common/SystemInfo.cs

@@ -43,6 +43,11 @@ namespace BizHawk.Client.Common
 
 		#region Get SystemInfo
 
+		/// <summary>
+		/// Gets the <see cref="SystemInfo"/> instance for Apple II
+		/// </summary
+		public static SystemInfo Libretro { get; } = new SystemInfo("Libretro", CoreSystem.Libretro, 1);
+
 		/// <summary>
 		/// Gets the <see cref="SystemInfo"/> instance for Apple II
 		/// </summary