[hwasan] An option to disable tag randomization.

Summary:
Avoid flaky test failures by by using a monotonic number sequence of
heap tags.

Does not affect stack tags: the way we generate those guarantees
uniqueness for at least 30-something first allocas in any function,
as well as the UAR tag.

Reviewers: alekseyshl, kcc

Subscribers: llvm-commits, kubamracek

Differential Revision: https://reviews.llvm.org/D41882

llvm-svn: 322214