_M_IX86 will be defined in mingw builds after including windows.h. as
the gcc inline asm is first, this missing check would only have caused
an error if the code was reorganized.
(cherry picked from commit 3fca851a202e5b1018a2cc491b9e005913394afe)
Change-Id: I395679bcfc43e94d308d1ceb0c0fbf932b2c378c
f4497a1ef5