SH optimized software floating point routines

[Joern Rennecke]

Quoting "Naveen H. S" <Naveen.S@kpitcummins.com>:

> extendsfdf2 - gcc.c-torture/execute/conversion.c
> gcc.dg/torture/fp-int-convert-float.c, gcc.dg/pr28796-2.c

Note that some tests invoke undefined behaviour; I've also come across this
when doing optimized soft FP for ARCompact:

http://gcc.gnu.org/viewcvs/branches/arc-4_4-20090909-branch/gcc/testsuite/gcc.dg/torture/fp-int-convert.h?r1=151539&r2=151545