Fix non-Windows platforms build break introduced by r355065. Fixes:

In file included from /home/buildbots/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/llvm/lib/Support/Memory.cpp:14:
/home/buildbots/ppc64le-lld-multistage-test/ppc64le-lld-multistage-test/llvm/include/llvm/Support/Memory.h:38:14: error: private field 'Flags' is not used [-Werror,-Wunused-private-field]
    unsigned Flags = 0;
             ^
1 error generated.

llvm-svn: 355066