The configure script in the three most recent releases of xorg-server define CWARNFLAGS without -fno-strict-aliasing.
In git, all versions of util/macros since version 1.2.0 define CWARNFLAGS with -fno-strict-aliasing. But these three releases have replaced that flag with -Wstrict-aliasing=2.
These releases were apparently created with a patched version of util/macros. Possibly the patch that is attached to the following bug report in comment #7:
The omission of -fno-strict-aliasing has caused a bug in Gentoo Linux involving xkb:
This has been fixed with xorg-server-1.9.2.tar.bz2.
on Feb 22, 2017 at 13:14:33.
(provided by the Example extension).