[NFC] Fix unused variable warning.

[dschuff]

How about just isa<WasmObjectFile>(&O) instead?

Otherwise, LGTM

[ncv]

Using isa<> rather than dyn_cast and discarding result.

llvm/lib/Object/SymbolSize.cpp

int llvm::object::compareAddress(const SymEntry *A, const SymEntry *B) {
   if (A->Address != B->Address)
     return A->Address < B->Address ? -1 : 1;
   return 0;
 }
 
 static unsigned getSectionID(const ObjectFile &O, SectionRef Sec) {
   if (auto *M = dyn_cast<MachOObjectFile>(&O))
     return M->getSectionID(Sec);
-  if (const auto *M = dyn_cast<WasmObjectFile>(&O))
+  if (isa<WasmObjectFile>(&O))
     return Sec.getIndex();
 
   return cast<COFFObjectFile>(O).getSectionID(Sec);
 }
 
 static unsigned getSymbolSectionID(const ObjectFile &O, SymbolRef Sym) {
   if (auto *M = dyn_cast<MachOObjectFile>(&O))
     return M->getSymbolSectionID(Sym);