Added LLVM_FALLTHROUGH to address warning: this statement may fall through. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304268 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-readobj/ELFDumper.cpp

@@ -2742,6 +2742,7 @@ std::string GNUStyle<ELFT>::getSymbolSectionNdx(const ELFO *Obj,
   case ELF::SHN_XINDEX:
     SectionIndex = unwrapOrError(object::getExtendedSymbolTableIndex<ELFT>(
         Symbol, FirstSym, this->dumper()->getShndxTable()));
+    LLVM_FALLTHROUGH;
   default:
     // Find if:
     // Processor specific