um: sysdep/barrier.h is not used for anything

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

diff --cc arch/um/os-Linux/signal.c
Simple merge

diff --cc arch/um/sys-x86/shared/sysdep/barrier.h
Simple merge

diff --cc arch/um/sys-x86/shared/sysdep/barrier_32.h
Simple merge

diff --cc arch/um/sys-x86/shared/sysdep/barrier_64.h
Simple merge