libpci: i386-io-windows.h: Do not define __readeflags() for GCC 4.9+

libpci: i386-io-windows.h: Do not define __readeflags() for GCC 4.9+

GCC header file <x86intrin.h> defines static inline function __readeflags()
which calls correct __builtin_ia32_readeflags_XX() builtin.

Header file <x86intrin.h> is included by MinGW-w64's <intrin.h> header file
in new versions of MinGW-w64 and <intrin.h> may be included transitionally
by some other header files automatically.

Defining __readeflags() as both macro and static inline function cause
compile errors.

Fix this compile error by not defining __readeflags() macro and instead
include GCC header file <x86intrin.h>.