Skip resetting the stack protector on eng builds

This CL will cause the Zygote to skip re-initialization of the stack
protector cookie on Eng builds.  This will prevent interpreter functions
that would not normally appear on the critical call path from causing
stack check failures.

Bug: 265760793
Test:  m libandroid_runtime (to ensure correct branch of pre-processor
conditional is taken)

Change-Id: I7ec7ac5a2230d1078c818013ae90f3d2597734a3