Remove initialize to zero on output variables for inline.

Remove initialize to zero on output variables for inline.

Inline that uses temporary variables is currently initializing them
to 0 and passing in as output "+r".
This CL replaces the output constraint to "=&r" for most meaning an
output with early write (before inputs).  This allows the initialize
to zero step to be removed, saving 1 instruction.

BUG=libyuv:580
TESTED=local libyuv build on gcc/linux and try bots
R=harryjin@google.com

Committed: https://chromium.googlesource.com/libyuv/libyuv/+/cf101116c977d8c452d2e5b690c30c04da7519c8

[harryjin, 2016-04-18 22:38:57]

lgtm

[fbarchard1, 2016-04-18 23:24:28]

Description was changed from

==========
Remove initialize to zero on output variables for inline.

Inline that uses temporary variables is currently initializing them
to 0 and passing in as output "+r".
This CL replaces the output constraint to "=&r" for most meaning an
output with early write (before inputs).  This allows the initialize
to zero step to be removed, saving 1 instruction.

BUG=libyuv:580
TESTED=local libyuv build on gcc/linux and try bots
R=harryjin@google.com
==========

to

==========
Remove initialize to zero on output variables for inline.

Inline that uses temporary variables is currently initializing them
to 0 and passing in as output "+r".
This CL replaces the output constraint to "=&r" for most meaning an
output with early write (before inputs).  This allows the initialize
to zero step to be removed, saving 1 instruction.

BUG=libyuv:580
TESTED=local libyuv build on gcc/linux and try bots
R=harryjin@google.com

Committed:
https://chromium.googlesource.com/libyuv/libyuv/+/cf101116c977d8c452d2e5b690c...
==========

[fbarchard1, 2016-04-18 23:24:30]

Committed patchset #3 (id:40001) manually as
cf101116c977d8c452d2e5b690c30c04da7519c8 (presubmit successful).