[MC][ELF] Fix gcc "enumeral and non-enumeral type in conditional expression" warning (NFC)

GCC warning:
```
/llvm-project/llvm/lib/MC/ELFObjectWriter.cpp: In member function ‘uint64_t {anonymous}::ELFWriter::writeObject(llvm::MCAssembler&, const llvm::MCAsmLayout&)’:
/llvm-project/llvm/lib/MC/ELFObjectWriter.cpp:1137:38: warning: enumeral and non-enumeral type in conditional expression [-Wextra]
 1137 |     write(uint32_t(Group->isComdat() ? ELF::GRP_COMDAT : 0));
      |                    ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
```