Asan use-after-scope: don't poison allocas if there were untraced lifetime...

Asan use-after-scope: don't poison allocas if there were untraced lifetime intrinsics in the function (PR41481)

If there are any intrinsics that cannot be traced back to an alloca, we
might have missed the start of a variable's scope, leading to false
error reports if the variable is poisoned at function entry. Instead, if
there are some intrinsics that can't be traced, fail safe and don't
poison the variables in that function.

Differential revision: https://reviews.llvm.org/D60686

llvm-svn: 358478