C#: Factor C++ parts out of autobuilder

cpp/autobuilder/Semmle.Autobuild.Cpp/CppAutobuilder.cs

@@ -0,0 +1,23 @@
+using Semmle.Autobuild.Shared;
+
+namespace Semmle.Autobuild.Cpp
+{
+    public class CppAutobuilder : Autobuilder
+    {
+        public CppAutobuilder(IBuildActions actions, AutobuildOptions options) : base(actions, options) { }
+
+        public override BuildScript GetBuildScript()
+        {
+            if (Options.BuildCommand != null)
+                return new BuildCommandRule((_, f) => f(null)).Analyse(this, false);
+
+            return
+                // First try MSBuild
+                new MsBuildRule().Analyse(this, true) |
+                // Then look for a script that might be a build script
+                (() => new BuildCommandAutoRule((_, f) => f(null)).Analyse(this, true)) |
+                // All attempts failed: print message
+                AutobuildFailure();
+        }
+    }
+}