Revert "afdo: Remove -fprofile-sample-accurate flag"

This reverts commit febf8b9b.

We are still seeing flaky performance alerts from microbenchmarks even
with this change, and this has caused binary size / memory usage
increase. Let's add this flag back and observe whether performance
regression reports become more frequent.

Change-Id: I0fec1296b1f49b21b59d81add677f6a926ee88dc