Optimize implementation of i32_set_cond using new macro-assembler
instruction LoadZeroOnCondition. This way, emitting branches is
avoided.

Bug: v8:6600
Change-Id: Icccb2f3714645851fac68a666ddb33db4a9d8062
Reviewed-on: https://chromium-review.googlesource.com/985976
Commit-Queue: Sreten Kovacevic <sreten.kovacevic@mips.com>
Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#52300}