tsan: remove unused pc arguments

Remove pc argument of ThreadIgnoreEnd, ThreadIgnoreSyncEnd
and AcquireGlobal functions. It's unused and in some places
we don't even have a pc and pass 0 anyway.
Don't confuse readers and don't pretend that pc is needed
and that passing 0 is somehow deficient.

Use simpler convention for ThreadIgnoreBegin and ThreadIgnoreSyncBegin:
accept only pc instread of pc+save_stack. 0 pc means "don't save stack".

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D106973