[Mesa-stable] Please pick commit 20553e4a2d95 to 12.0

[Matt Turner]

Meant to tag it for stable:

commit 20553e4a2d952f6dc37f40f63d2c86b0718c58f9
Author: Matt Turner <mattst88 at gmail.com>
Date:   Thu Jul 21 11:46:23 2016 -0700

    mesa: Use AC_HEADER_MAJOR to include correct header for major().

    Gentoo has been smoke testing an upcoming change to glibc.

    Bugzilla: https://bugs.gentoo.org/show_bug.cgi?id=580392