Draft: nativeGen: Deduplicate DWARF strings
As noted in #17609, we previously made no attempt to deduplicate strings. This resulted in unnecessarily long compile times and large object files. Fix this.
Furthermore, while working on this I noticed that there is frighteningly-little
protection against overflowing the range of Unique
(#18918). Fix this by adding
overflow checks on 32-bit platforms and DEBUG compilers.
Fixes #17609.