BACKPORT: FROMGIT: kbuild: mkcompile_h: Include version

 in /proc/version

When doing Clang builds of the kernel, it is possible to link with
either ld.bfd (binutils) or ld.lld (LLVM), but it is not possible to
discover this from a running kernel. Add the ' -v' output to
/proc/version.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jprimero15 <jprimero155@gmail.com>