Change our ELF binary branding to something more acceptable to the Binutils

Change our ELF binary branding to something more acceptable to the Binutils
maintainers.

After we established our branding method of writing upto 8 characters of
the OS name into the ELF header in the padding; the Binutils maintainers
and/or SCO (as USL) decided that instead the ELF header should grow two new
fields -- EI_OSABI and EI_ABIVERSION.  Each of these are an 8-bit unsigned
integer.  SCO has assigned official values for the EI_OSABI field.  In
addition to this, the Binutils maintainers and NetBSD decided that a better
ELF branding method was to include ABI information in a ".note" ELF
section.

With this set of changes, we will now create ELF binaries branded using
both "official" methods.  Due to the complexity of adding a section to a
binary, binaries branded with ``brandelf'' will only brand using the
EI_OSABI method.  Also due to the complexity of pulling a section out of an
ELF file vs. poking around in the ELF header, our image activator only
looks at the EI_OSABI header field.

Note that a new kernel can still properly load old binaries except for
Linux static binaries branded in our old method.

  *
  * For a short period of time, ``ld'' will also brand ELF binaries
  * using our old method.  This is so people can still use kernel.old
  * with a new world.  This support will be removed before 5.0-RELEASE,
  * and may not last anywhere upto the actual release.  My expiration
  * time for this is about 6mo.
  *