mingw-w64-crt/intrincs/currentfiber.c - mingw-w64 - Git at Google

 #ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
 #endif
 #include <windows.h>

  PVOID GetCurrentFiber(VOID)
  {
    return(PVOID)__readgsqword(FIELD_OFFSET(NT_TIB,FiberData));
  }
	#ifndef WIN32_LEAN_AND_MEAN
	#define WIN32_LEAN_AND_MEAN
	#endif
	#include <windows.h>

	PVOID GetCurrentFiber(VOID)
	{
	return(PVOID)__readgsqword(FIELD_OFFSET(NT_TIB,FiberData));
	}