[tools] Remove unused local variables (NFC) (#138384)

Author: kazutakahirata

llvm/tools/llvm-lto/llvm-lto.cpp

@@ -1136,7 +1136,6 @@ int main(int argc, char **argv) {
     if (SaveLinkedModuleFile) {
       std::string ModuleFilename = OutputFilename;
       ModuleFilename += ".linked.bc";
-      std::string ErrMsg;
 
       if (!CodeGen.writeMergedModules(ModuleFilename))
         error("writing linked module failed.");
@@ -1150,7 +1149,6 @@ int main(int argc, char **argv) {
     if (SaveModuleFile) {
       std::string ModuleFilename = OutputFilename;
       ModuleFilename += ".merged.bc";
-      std::string ErrMsg;
 
       if (!CodeGen.writeMergedModules(ModuleFilename))
         error("writing merged module failed.");

llvm/tools/llvm-objdump/SourcePrinter.cpp

@@ -378,7 +378,6 @@ void SourcePrinter::printSourceLine(formatted_raw_ostream &OS,
   DILineInfo LineInfo = DILineInfo();
   Expected<DILineInfo> ExpectedLineInfo =
       Symbolizer->symbolizeCode(*Obj, Address);
-  std::string ErrorMessage;
   if (ExpectedLineInfo) {
     LineInfo = *ExpectedLineInfo;
   } else if (!WarnedInvalidDebugInfo) {

llvm/tools/llvm-readobj/llvm-readobj.cpp

@@ -276,7 +276,6 @@ static void parseOptions(const opt::InputArgList &Args) {
   opts::ProgramHeaders = Args.hasArg(OPT_program_headers);
   opts::SectionGroups = Args.hasArg(OPT_section_groups);
   if (Arg *A = Args.getLastArg(OPT_sort_symbols_EQ)) {
-    std::string SortKeysString = A->getValue();
     for (StringRef KeyStr : llvm::split(A->getValue(), ",")) {
       SortSymbolKeyTy KeyType = StringSwitch<SortSymbolKeyTy>(KeyStr)
                                     .Case("name", SortSymbolKeyTy::NAME)