tsan: enable sse4.2 in tests

Pass -msse4.2 flag to the tests the same way we do for the runtime.
Layout of some structs in the runtime headers depends on the flag
(TSAN_VECTORIZE), so we need it to be consistent across the runtime
and tests.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D110192