kvm tools: prevent the redefined error

In file included from ../../include/linux/stddef.h:4:0,
                 from ../../include/linux/list.h:5,
                 from include/kvm/framebuffer.h:5,
                 from builtin-run.c:8:
include/linux/compiler.h:8:0: error: "__attribute_const__" redefined [-Werror]
/usr/include/sys/cdefs.h:226:0: note: this is the location of the previous definition
cc1: all warnings being treated as errors

make: *** [builtin-run.o] Error 1

Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>