[dsymutil] Prevent use-after-free
The BinaryHolder would query the archive member MemoryBuffer name
to check if the current open archive also contains the next requested
objectfile. This comparison was using a StringRef to a temporary
buffer. It only happened with fat archives. This commit adds long-lived
storage along with the MemoryBuffers for the fat archive filename.
The added test would fail during an ASAN build without the fix.