Differences in build options for libg and libg-nano

By browsing the build script I noticed that libg and libg-nano are build with one strange difference. For "normal" gcc (and libg) compilation in "gcc-final" step this is passed to make:

INHIBIT_LIBC_CFLAGS="-DUSE_TM_CLONE_REGISTRY=0"

On the other hand, no such option is passed to compilation in the "gcc-size-libstdcxx" step (which builds libg-nano). Is this intentional or maybe a mistake? Shouldn't both libs have this option identical? Maybe this options is not important and could be removed from the "normal" gcc build ("gcc-final" step)?

BTW - could you tell me what this option does? I was browsing the net for USE_TM_CLONE_REGISTRY and only found info that it has something to do with "transactional memory", but no explanation which would tell me whether I want that option or not (;

Thanks in advance!