Included the headers for AST tests to the solution. (#881)

Fixes #850

src/Generator.Tests/premake5.lua

@@ -12,6 +12,11 @@ project "CppSharp.Generator.Tests"
     depsdir .. "/NSubstitute"
   }
 
+  files { testsdir .. "/Native/AST.h", testsdir .. "/Native/ASTExtensions.h", testsdir .. "/Native/Passes.h" }
+  filter "files:**.h"
+     buildaction "None"
+  filter {}
+
   SetupParser()
 
   links