This patch removes one unnecessary sub instruction in ComputeCodeStartAddress for SpeculationPoison generation at the beginning of each bytecode handler.

leaq rbx,[rip+0x0]      => leaq rbx,[rip+0xfffffff9]
subq rbx,0x7            => To be removed
movq r9,0x0
cmpq rcx,rbx
movq rbx,0xffffffff
cmovzq r9,rbx


Change-Id: I7648ae27d4039488d1fc0f4c25477a5cb889bd6d
Reviewed-on: https://chromium-review.googlesource.com/933593Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Shiyu Zhang <shiyu.zhang@intel.com>
Cr-Commit-Position: refs/heads/master@{#51537}