Documentation: disable vdso_test to avoid breakage with old glibc

glibc versions older than 2.16 don't include sys/auxv.h which this
executable uses.
Since we don't have a good way to test for specific glibc versions in
kbuild, just disable it for now.
Signed-off-by: Peter Foley <pefoley2@pefoley.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/vDSO/Makefile

-# List of programs to build
-hostprogs-y := vdso_test
+# vdso_test won't build for glibc < 2.16, so disable it
+# hostprogs-y := vdso_test
 hostprogs-$(CONFIG_X86) := vdso_standalone_test_x86
 vdso_standalone_test_x86-objs := vdso_standalone_test_x86.o parse_vdso.o
 vdso_test-objs := parse_vdso.o vdso_test.o