Add support for a partial ubsan build.

Some of the ubsan checks expose a few pathological performance cases
in clang, and thus aren't suited to be used in SANITIZE_HOST.

This mode is also supported on the target despite not having the
target runtime libraries for ubsan by generating traps.

Change-Id: I0b0f0a08ca84d72e44e2174a66726b1c5e5cad7e