I am in the process of migrating an NDK application from AOSP 7 to 8 and right away I have two (related) issues.
1) I used to build my module with mm -B, but now it seems -B is no longer an accepted option.
2) How can I do a clean of just my module? This answer was pre AOSP 8 and instructed doing an mm -B which is no longer an option.
The short answer is that you don't. Soong tracks dependencies properly (unlike our old make system) so you don't ever need to do the equivalent of mm -B. If you find any cases to the contrary that's a bug.