For pc-rel fixups, we have a ConstantRelocatable referring
to Foo+0, and and the offset "-4" is encoded in the code
buffer (but not the ConstantRelocatable object). Thus we
need to load from the code buffer in order to
get that "-4" instead of just taking the +0 from Foo+0.

For non-pc-rel fixups, we have the ConstantRelocatable
with a true offset, and we also write that offset into the
code buffer (for ELF REL and not RELA, it expects the
offset in the code buffer). In this case, we want to choose
one and not double-count.

BUG=none
176.gcc seemed to be failing when compiled with --filetype=iasm...
load address for 64-bit pointers were +8 instead of +4

R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1241313002 .