We should not include glibc headers from BIOS code which can't rely on glibc at
runtime.

This patch fixes the following build breakage on 64-bit:

    CC       bios/e820.o
  In file included from /usr/include/features.h:387:0,
                   from /usr/include/unistd.h:26,
                   from include/kvm/util.h:12,
                   from bios/e820.c:5:
  /usr/include/gnu/stubs.h:7:27: fatal error: gnu/stubs-32.h: No such file or directory compilation terminated.
  make: *** [bios/bios.bin.elf] Error 1

when built without the 'glibc-devel.i686' package on Fedora, for example.

Cc: Asias He <asias.hejun@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Sasha Levin <levinsasha928@gmail.com>
Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>