[llvm-objcopy] Preserve .ARM.attributes section when stripping files

This works around a bug in Debian's patchset for glibc. The bug is
described in detail in the upstream debian bug:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=943798, but the short
version of it is that glibc on any Debian based distro don't load
libraries unless it has a .ARM.attribute section.

Reviewed by: jhenderson, rupprecht, MaskRay, jakehehrlich

Differential Revision: https://reviews.llvm.org/D69188

Patch by Tobias Hieta.

(cherry picked from commit fb4a55010ee9bd03720609c8542f770775576fc8)