Make 32-bit member offset in Archive::Symbol::getMember 64-bit

[jakehehrlich]

Summary

When accessing a member for a symbol with an offset greater than 2^32 - 1 the current Archive::Symbol::getMember implementation will overflow and cause unexpected behavior. This change simply fixes that. In particular if you call "llvm-nm --print-armap" on an archive that has this behavior you'll get an error.

lib/Object/Archive.cpp

 
 Expected<Archive::Child> Archive::Symbol::getMember() const {
   const char *Buf = Parent->getSymbolTable().begin();
   const char *Offsets = Buf;
   if (Parent->kind() == K_GNU64 || Parent->kind() == K_DARWIN64)
     Offsets += sizeof(uint64_t);
   else
     Offsets += sizeof(uint32_t);
-  uint32_t Offset = 0;
+  uint64_t Offset = 0;
   if (Parent->kind() == K_GNU) {
     Offset = read32be(Offsets + SymbolIndex * 4);
   } else if (Parent->kind() == K_GNU64) {
     Offset = read64be(Offsets + SymbolIndex * 8);
   } else if (Parent->kind() == K_BSD) {
     // The SymbolIndex is an index into the ranlib structs that start at
     // Offsets (the first uint32_t is the number of bytes of the ranlib
     // structs).  The ranlib structs are a pair of uint32_t's the first