Support for native bool on Visual C++ build

[matthiasblaesing]

Currently the unittest NativeTest#testSizeof fails for bool when the binaries are build with the Microsoft SDK for Windows 7.1. The problem is located in dispatch.c: (line 123):

#ifdef __cplusplus
extern "C" {
#else
#if defined(_MSC_VER)
// At least until I upgrace to 2013-era MSVS
typedef int bool;
#define true 1
#define false 0
#else
#include <stdbool.h>
#endif
#endif

in this case the defined bool type has the same size as int (4 bytes), which conflicts with mingw + gcc (both 1).