x86, relocs: Workaround for binutils 2.22.52.0.1 section bug

GNU ld 2.22.52.0.1 has a bug that it blindly changes symbols from
section-relative to absolute if they are in a section of zero length.
This turns the symbols __init_begin and __init_end into absolute
symbols.  Let the relocs program know that those should be treated as
relative symbols.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: H.J. Lu <hjl.tools@gmail.com>