fp-bit.h (MAX_USI_INT, MAX_SI_INT): Don't assume unsigned is wide enough.

* config/fp-bit.h (MAX_USI_INT, MAX_SI_INT): Don't assume
unsigned is wide enough.
(BITS_PER_SI): New.
* config/fp-bit.c (_fpmul_parts): Don't assume 32-bits SI.
(si_to_float): Likewise.
(float_to_si, float_to_usi): Use BITS_PER_SI.

From-SVN: r39407