soft-fp extensions and sNaNs

[David Miller]

The new test added to math/basic-test.c since glibc-2.18 fails on
sparc for the quad float cases that use soft-fp:

Failure:  long double x = (long double) (float) sNaN, !issignaling
Failure:  long double x = (long double) (double) sNaN, !issignaling

Looking specifically at 32-bit sparc's q_dtoq.c it seems to be
implemented identically to soft-fp/extenddftf2.c, so this appears to
be a generic soft-fp issue.

Joseph have you run into this already or know about it?