Similar to https://freedesktop.org/patch/34699/:

libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I.. -fvisibility=hidden -I/usr/include/xorg -I/usr/include/pixman-1 -I/usr/include/X11/dri -I/usr/include/libdrm -fvisibility=hidden -I/usr/include/xorg -I/usr/include/pixman-1 -I/usr/include/X11/dri -I/usr/include/libdrm -I/usr/include/libdrm -I/usr/include/X11/dri -g -O2 -MT via_3d.lo -MD -MP -MF .deps/via_3d.Tpo -c via_3d.c  -fPIC -DPIC -o .libs/via_3d.o
In file included from /usr/include/string.h:634:0,
                 from /usr/include/xorg/os.h:53,
                 from /usr/include/xorg/misc.h:115,
                 from /usr/include/xorg/xf86str.h:37,
                 from /usr/include/xorg/xf86.h:44,
                 from via_3d.h:27,
                 from via_3d.c:24:
/usr/include/xorg/os.h:579:1: error: expected identifier or ‘(’ before ‘__extension__’
 strndup(const char *str, size_t n);
 ^
Makefile:585: recipe for target 'via_3d.lo' failed


solution: in via_3d.h add:

#include "xorg-server.h"

before:

#include "xf86.h"