[llvm-objdump] Should print unknown d_tag in hex format

Summary:
Currently, `llvm-objdump` prints "unknown" instead of d_tag value in hex format. Because getDynamicTagAsString returns "unknown" rather than empty 
string.

Reviewers: grimar, jhenderson

Reviewed By: jhenderson

Subscribers: rupprecht, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58763

llvm-svn: 355262
diff --git a/llvm/tools/llvm-objdump/ELFDump.cpp b/llvm/tools/llvm-objdump/ELFDump.cpp
index 6734f76..c358b42 100644
--- a/llvm/tools/llvm-objdump/ELFDump.cpp
+++ b/llvm/tools/llvm-objdump/ELFDump.cpp
@@ -176,15 +176,8 @@
     if (Dyn.d_tag == ELF::DT_NULL)
       continue;
 
-    StringRef Str = StringRef(Elf->getDynamicTagAsString(Dyn.d_tag));
-
-    if (Str.empty()) {
-      std::string HexStr = utohexstr(static_cast<uint64_t>(Dyn.d_tag), true);
-      outs() << format("  0x%-19s", HexStr.c_str());
-    } else {
-      // We use "-21" in order to match GNU objdump's output.
-      outs() << format("  %-21s", Str.data());
-    }
+    std::string Str = Elf->getDynamicTagAsString(Dyn.d_tag);
+    outs() << format("  %-21s", Str.c_str());
 
     const char *Fmt =
         ELFT::Is64Bits ? "0x%016" PRIx64 "\n" : "0x%08" PRIx64 "\n";