Fix warning about #pragma once in source file.
Fix warning about #pragma once in source file.

zillemarco/CppSharp,mono/CppSharp,ddobrev/CppSharp,zillemarco/CppSharp,mono/CppSharp,zillemarco/CppSharp,mono/CppSharp,ddobrev/CppSharp,mono/CppSharp,ddobrev/CppSharp,mono/CppSharp,zillemarco/CppSharp,zillemarco/CppSharp,ddobrev/CppSharp,ddobrev/CppSharp,mono/CppSharp