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

 #define __INTRINSIC_ONLYSPECIAL
 #define __INTRINSIC_SPECIAL___readfsbyte // Causes code generation in intrin-impl.h

 #include <intrin.h>
	#define __INTRINSIC_ONLYSPECIAL
	#define __INTRINSIC_SPECIAL___readfsbyte // Causes code generation in intrin-impl.h

	#include <intrin.h>