In libspatialite 4.3.0a, config.sub/config.guess are very old (timestamp='2009-11-20').  This prevents building for newer architectures.  For example,

./configure --build=x86_64-linux-gnu --host=aarch64-linux-gnu
...
checking host system type... Invalid configuration `aarch64-linux-gnu': machine `aarch64' not recognized
configure: error: ./config.sub aarch64-linux-gnu failed

If I update to the latest config.sub/config.guess (from with timestamp='2020-07-12'), I'm able to build for more arches (such as aarch64).

libspatialite should update to the latest config.sub/config.guess so we don't have to do these workarounds.