Bisect tool: Use symbolic link for replacing object files on Android

The bisection tool used hard link to replace object files from good/bad
set on Android. I do not see why it is necessary to use hard link than
symbolic one, and it will introduce hidden bug if try to link one obj
from one disk to the other.

Test=Tested with Android and succeeded.
Bug=None

Change-Id: If0a1f7f0736052547462fadc955587092dada722
Reviewed-on: https://chromium-review.googlesource.com/1260251
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Zhizhou Yang <zhizhouy@google.com>
Reviewed-by: Caroline Tice <cmtice@chromium.org>
2 files changed