Add an UBSAN implementation and a new UBSAN switch to the make build.
The implementation is taken from Onyx and handles most of the cases
that should be needed for a kernel build. Floating point and fancy
C++ CFI features are not supported yet.
To build with UBSAN, pass UBSAN=1 to make such as:
PROJECT=pc-x86-64-test make -jN UBSAN=1
