The AOSP master branch is already reflecting the 2021 work in progress.
Host C/C++ builds in Make have been deprecated, and are errors by default (but are still available behind BUILD_BROKEN_USES_BUILD_* flags). Lesser used module types (AUX, NATIVE_BENCHMARK, STATIC_TEST_LIBRARY) are also in that state. [HOST_]SHARED_TEST_LIBRARY was removed because it was previously marked obsolete.
The rest of the module types are still available, but as before, there may be other reasons you need to switch code to Android.bp -- if something else that was converted to Android.bp needs to link to your library, your library needs to be in an Android.bp; if you are defining a jar to put in the bootclasspath; etc.
- Dan