How do I get Base System to rebuild?

I'm trying to get a GCC libc build up and running to use the address sanitiser capabilities. If I have built a target image and then use menuconfig to add things like libasan and liblsan they don't get built unless I do a dirclean to remove the toolchain. Is that intended, and is there still a way to get those libraries built without such a drastic step?

OpenWrt uses MUSL by default? So, if you built an image and changed from MUSL to GCC, you would need to recompile the toolchain. Once you compile under GCC toolchain, you shouldn't need to dirclean/distclean unless it changes

Maybe I'm misunderstanding which bit doesn't seem to rescan .config.

I do a distclean, then a make menuconfig where I choose target device plus set some developer options to select glibc. That gets me a flashable image.

I then want to start tinkering with Address Sanitizer, so use menuconfig to select ASAN and LSAN libraries in Base System. But a make doesn't seem to build the new libs.

If I do a dirclean and then make I seem to get ASAN built, but not LSAN.

It's hard to tell if this is expected behaviour or not as I can't find any references to others using glibc rather than MUSL.