[llvm-readobj/MachO] Ensure we always have a valid reference to SegmentName

[davide]

Summary

This way we don't end up printing garbage. Found while testing lld-macho.

[davide]

git-clang-format.

[grosbach]

Interesting. Would it be better to change the StringRef to a std::string instead? That way the data structure itself maintains the full info.

[davide]

I think it's a good idea (we should probably do the same for Section, but we can take care of that in a separate commit).

Thanks!

[grosbach]

LGTM

llvm/trunk/tools/llvm-readobj/MachODumper.cpp

struct MachOSection {
     uint32_t NumRelocationTableEntries;
     uint32_t Flags;
     uint32_t Reserved1;
     uint32_t Reserved2;
     uint32_t Reserved3;
   };
 
   struct MachOSegment {
-    StringRef CmdName;
-    StringRef SegName;
+    std::string CmdName;
+    std::string SegName;
     uint64_t cmdsize;
     uint64_t vmaddr;
     uint64_t vmsize;
     uint64_t fileoff;
     uint64_t filesize;
     uint32_t maxprot;
     uint32_t initprot;
     uint32_t nsects;