tsan: always setup sigaction signal handler

Currently we setup either sigaction signal handler with 3 arguments
or old style signal handler with 1 argument depending on user handler type.
This unnecessarily complicates code. Always setup sigaction handler.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D107186

GitOrigin-RevId: 53a526790d841beb04294f232982796d0803dd3c