[Bug c/60847] x86 BMI intrinsics not recognized

[spatel at rotateright dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60847

--- Comment #1 from Sanjay Patel <spatel at rotateright dot com> ---
It looks like an extra leading underscore is required to recognize the BMI
intrinsics. This is not happening with other (BMI2, SSE4) intrinsics. 

According to the Intel reference docs and previous versions of gcc, a single
underscore is the correct usage.