x86: enable compatible 32 C/R back

Supported only from v4.9 kernel :)

The following commits may be backported if needed:
b059a453b ("x86/vdso: Add mremap hook to vm_special_mapping")
e38447ee1 ("x86/vdso: Unmap vdso blob on vvar mapping failure")
576ebfefd ("x86/vdso: Replace calculate_addr in map_vdso() with addr")
2eefd8789 ("x86/arch_prctl/vdso: Add ARCH_MAP_VDSO_*")
90954e7b9 ("x86/coredump: Use pr_reg size, rather that TIF_IA32 flag")
cc87324b3 ("x86/ptrace: Down with test_thread_flag(TIF_IA32)")
684635105 ("x86/signal: Add SA_{X32,IA32}_ABI sa_flags")
ed1e7db33 ("x86/signal: Remove bogus user_64bit_mode() check from
sigaction_compat_abi()")

The required patches list may be checked also at
https://criu.org/Upstream_kernel_commits



travis-ci: success for Rectify 32-bit compatible C/R on x86
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>