[ORC] Fix heap-use-after-free error in MachODebugObjectSynthesizer.cpp

At line 191, `addSymbol` takes the name by reference but does not make
an internal copy to the string, meaning the local
`optional<std::string>` would get freed and leave Orc with a dangling
pointer. Fix this by just using an `optional<StringRef>` instead.

GitOrigin-RevId: 4b13c86d980af81fb9badc1b6b88f77f4faf5e53
1 file changed