If MSBuild 12.0 is installed, use it for all .NET 4.x projects.

src/Main/Base/Project/Util/DotnetDetection.cs

@@ -69,5 +69,16 @@ namespace ICSharpCode.SharpDevelop
 			}
 			return null;
 		}
+		
+		/// <summary>
+		/// Gets whether the Microsoft Build Tools 2013 (MSBuild 12.0) is installed.
+		/// </summary>
+		public static bool IsBuildTools2013Installed()
+		{
+			// HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DevDiv\BuildTools\Servicing\12.0
+			using (var key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\DevDiv\BuildTools\Servicing\12.0\MSBuild")) {
+				return key != null && key.GetValue("Install") as int? >= 1;
+			}
+		}
 	}
 }

src/Main/SharpDevelop/Project/Build/MSBuildEngine/MSBuildEngineWorker.cs

@@ -159,10 +159,12 @@ namespace ICSharpCode.SharpDevelop.Project
 					loggerChain.HandleError(new BuildError(job.ProjectFileName, ".NET 3.5 SP1 is required to build this project."));
 					tcs.SetResult(false);
 				}
-			} else if (projectMinimumSolutionVersion <= SolutionFormatVersion.VS2010) {
-				BuildWorkerManager.MSBuild40.RunBuildJob(job, loggerChain, OnDone, cancellationToken);
 			} else {
-				BuildWorkerManager.MSBuild120.RunBuildJob(job, loggerChain, OnDone, cancellationToken);
+				if (DotnetDetection.IsBuildTools2013Installed()) {
+					BuildWorkerManager.MSBuild120.RunBuildJob(job, loggerChain, OnDone, cancellationToken);
+				} else {
+					BuildWorkerManager.MSBuild40.RunBuildJob(job, loggerChain, OnDone, cancellationToken);
+				}
 			}
 			return tcs.Task;
 		}