[asan] Avoid lifetime analysis for allocas with can be in ambiguous state

Summary:
C allows to jump over variables declaration so lifetime.start can be
avoid before variable usage. To avoid false-positives on such rare cases
we detect them and remove from lifetime analysis.

PR27453
PR28267

Reviewers: eugenis

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D24321

llvm-svn: 280907