Title: [TSAN] Parameterize the hard-coded threshold of deflake in tsan test

Summary:
A number of testcases in TSAN are designed to deal with intermittent problems
not exist in all executions of the tested program. A script called deflake.bash
runs the executable up to 10 times to deal with the intermittent nature of the tests.

The purpose of this patch is to parameterize the hard-coded threshold above via
--cmake_variables=-DTSAN_TEST_DEFLAKE_THRESHOLD=SomeIntegerValue
When this cmake var is not set, the default value of 10 will be used.

Reviewer: dvyukov (Dmitry Vyukov), eugenis (Evgenii Stepanov), rnk (Reid Kleckner), hubert.reinterpretcast (Hubert Tong), vitalybuka (Vitaly Buka)

Reviewed By: vitalybuka (Vitaly Buka)

Subscribers: mgorny (Michal Gorny), jfb (JF Bastien), steven.zhang (qshanz), llvm-commits (Mailing List llvm-commits), Sanitizers

Tag: LLVM, Sanitizers

Differential Revision: https://reviews.llvm.org/D73707