Reapply r329859 (partially, by imp):

Do not include float interfaces when using libsa.

We don't support float in the boot loaders, so don't include
interfaces for float or double in systems headers. In addition, take
the unusual step of spiking double and float to prevent any more
accidental seepage.

(cherry picked from commit 8630bfad40a427d0ab21d9f051c876480ad15dc2)