[clang] Fix -Wsubobject-linkage after D117262

/home/buildbot/llvm-avr-linux/llvm-avr-linux/llvm/clang/lib/CodeGen/Address.h:76:7: warning: 'clang::CodeGen::Address' has a field 'clang::CodeGen::Address::A' whose type uses the anonymous namespace [-Wsubobject-linkage]

https://lab.llvm.org/buildbot/#/builders/112/builds/12047