Subzero. Adds a pass for target-specific helper call generation.

Subzero. Adds a pass for target-specific helper call generation.

This pass gives Targets the ability to pre-lower high-level
instructions that will later be lowered to a target-specific helper,
e.g., 64-bit division on targets that can't natively handle them.

This is a pre-requirement for correct outargs pre-allocation during
function prolog.

R=sehr@chromium.org

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=5e0a8a71b75ec56981883587612b16f7c1635a03

[John, 2015-11-20 19:08:18]

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

[sehr, 2015-11-20 19:24:55]

lgtm

[John, 2015-11-20 21:50:41]

Committed patchset #1 (id:1) manually as
5e0a8a71b75ec56981883587612b16f7c1635a03 (presubmit successful).