xsave: check for X86_FEATURE_OSXSAVE rather than for X86_FEATURE_XSAVE

Migrating a process between a system with the 'xsave' CPU flag and
another system without the 'xsave' CPU flags is not possible and
fails during restore. To avoid this situation it is possible to boot
the source system of the migration with 'noxsave' kernel command-line.

Unfortunately criu currently tries to detect the presence of 'xsave'
with the macro X86_FEATURE_XSAVE which represents the features of
the CPU without taking into account if the operating system has
disabled 'xsave'. Checking for 'xsave' availability with the macro
X86_FEATURE_OSXSAVE detects correctly if Linux has been booted
with disabled 'xsave' and thus migrating processes between hosts
with and without 'xsave' is possible if the kernel uses the flag
'noxsave'.

travis-ci: success for criu dump fails when using noxsave (rev2)
Signed-off-by: Adrian Reber <areber@redhat.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>