[ASAN] Make sure we are only processing lifetime markers with offset 0 to alloca

This patch addresses https://bugs.llvm.org/show_bug.cgi?id=47787 (and hence https://bugs.llvm.org/show_bug.cgi?id=47767 as well).
In latter instrumentation code, we always use the beginning of the alloca as the base for instrumentation, ignoring any offset into the alloca.
Because of that, we should only instrument a lifetime marker if it's actually pointing to the beginning of the alloca.

Differential Revision: https://reviews.llvm.org/D89191