Fixed causing undefined symbols related minimum requirements for il2c…

… runtimes. #99

IL2C.Core/Writers/HeaderWriter.cs

@@ -177,6 +177,8 @@ public static void WriteCommonHeader(
                 twHeader.SplitLine();
                 twHeader.WriteLine("#pragma once");
                 twHeader.SplitLine();
+                twHeader.WriteLine("#include <il2c.h>");
+                twHeader.SplitLine();
 
                 // Write assembly references.
                 var assemblies = extractContext.EnumerateDeclaredTypes().

IL2C.Runtime/include/IL2C.Interop.h

@@ -0,0 +1,29 @@
+/////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// IL2C - A translator for ECMA-335 CIL/MSIL to C language.
+// Copyright (c) 2016-2019 Kouji Matsui (@kozy_kekyo, @kekyo2)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+/////////////////////////////////////////////////////////////////////////////////////////////////
+
+#ifndef IL2C_Interop_dll_H__
+#define IL2C_Interop_dll_H__
+
+#pragma once
+
+// IL2C.Interop.dll contains mostly usable IL2C/Invoke definitions
+// with private knowledge.
+#include <il2c.h>
+
+#endif