GB_NO_WINDOWS_H doesn't compile

[lackhoa]

The Windows version of gbMutex still depends on CRITICAL_SECTION, which is in windows.h.

// Mutex
typedef struct gbMutex {
#if defined(GB_SYSTEM_WINDOWS)
	CRITICAL_SECTION win32_critical_section;
#else
	pthread_mutex_t pthread_mutex;
	pthread_mutexattr_t pthread_mutexattr;
#endif
} gbMutex;