Fix some issues with Mips16 floating when certain intrinsics are present.

This is actually an LLVM bug in the way it generates signatures for these
when soft float is enabled. For example, floor ends up having the signature
of int64(int64). The signature part is not the same as where the actual
parameter types are recorded, and those ARE of course int64(int64) when
soft float is enabled. (Yes, Mips16 hard float uses soft float but with
different runtime rounes but then has to interoperate with Mips32 using
normal floating point). This logic will eventually be moved to the 
Mips16HardFloat pass so it's not worth sorting out these issues in LLVM
since nobody but Mips16 cares about these signatures, as far as I know,
and even I won't eventually either.

llvm-svn: 187613