intrin-impl.h: do not define _xgetbv for GCC 8

GCC 8 from r248028 has defined function _xgetbv and we should
avoid double definition of this function.

Signed-off-by: Mateusz Brzostek <mateuszb@poczta.onet.pl>
Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit 3ce3e27f044935f19e93e80c43ca695262d484e1)
Signed-off-by: Jonathan Yong <10walls@gmail.com>
1 file changed