[HWASAN] Untag before tagging alloca pointers

[HWASAN] Untag before tagging alloca pointers

This is folloup to b5595836, which missed the
Replacemen variable.

Before b5595836 the code assumed that alloca
ptrs are not tagged so tagging is implemented
as simple OR.

So this patch completes support of tagged SP
by passing untagged alloca pointers into
tagPointer.