`DlSymAllocator` allows early allocations, when
tsan is not yet initialized, e.g. from `dlsym`.
All other sanitizers with interceptors already use
`DlSymAllocator`.
Existing `in_symbolizer()` tsan logic is very similar.
However, we need to keep both as `DlSymAllocator`
does not support large allocations, needed for Symolizer.