Subzero: Fix dependency checking to avoid unnecessary rebuilds.

Subzero: Fix dependency checking to avoid unnecessary rebuilds.

When trying to do bisection debugging, the pnacl-llc translation was happening every time even if the pexe didn't change.  This is because it was checking for a binary called 'llc' in the current directory, instead of an absolute path the pnacl-llc.  (This check is done so that updating pnacl-llc triggers a rebuild of the bisection binary, similar to the check for an update of pnacl-sz.)

BUG= none
R=jvoung@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=8c7b0a2ce1e91d170d0f225e6e911cd20956d4e9

[Jim Stichnoth, 2015-03-29 00:14:50]

stichnot@chromium.org changed reviewers:
+ jvoung@chromium.org, kschimpf@google.com

[jvoung (off chromium), 2015-03-29 19:03:58]

lgtm

[Jim Stichnoth, 2015-03-29 22:20:42]

Committed patchset #1 (id:1) manually as
8c7b0a2ce1e91d170d0f225e6e911cd20956d4e9 (presubmit successful).