um: Remove copy&paste code from init.h

As we got rid of the __KERNEL__ abuse, we can directly
include linux/compiler.h now.
This also allows gcc 5 to build UML.

Change-Id: I07de22048076dfb3c191854dc7b70b81a8a84c8c
Reported-by: Hans-Werner Hilse <hwhilse@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Git-commit: 30b11ee9ae23d78de66b9ae315880af17a64ba83
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Srinivasarao P <spathi@codeaurora.org>