[Bug fortran/67531] No IEEE rounding support for powerpc long double type

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67531

--- Comment #9 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to David Edelsohn from comment #7)
> What progress do you expect?  IBM long double does not support non-default
> rounding.  This will be fixed when PPC64LE long double defaults to IEEE 128
> bit floating point.

ieee_arithmetic.F90 can be enhanced to pass "kind" argument to
support_fpu_rounding_mode, so it would be defined in fpu-glibc.h as:

int
support_fpu_rounding_mode (int mode, int kind)

Using some #ifdeffery (involving __powerpc__ and __float128), the function
could return 0 for unsupported kinds.

Please see how underflow control is handled in fpu-glibc.h for alpha, where
target supports underflow control only for 32bit and 64bit hardware floats, not
for 128bit soft-fp floats.