[CSSPGO][llvm-profgen] Ignore LBR records after interrupt transition

If we have seen an inwards transition from external code to internal code, but not a following outwards transition, the inwards transition is likely due to interrupt which is usually unpaired. Ignore current  and subsequent entries since they are likely from an unrelated pre-interrupt context.

LBR records from different interrupt context are unrelated and they should not be mixed together. Currenlty the OS does this for task-scheduling interrupt but not for all interrupts.

Reviewed By: wenlei, wlei

Differential Revision: https://reviews.llvm.org/D104276