frange: add both zeros to ranges when there's the possiblity of equality.
Every time there's equality at play, we must be careful that any
equality with zero matches both -0.0 and +0.0 when honoring signed
zeros.
We were doing this correctly for the == and != op1_range operators
(albeit inefficiently), but aren't doing it at all when building >=
and <=. This fixes the oversight.
There is change in functionality here for the build_* functions.
This is the last "simple" patch I submit before overhauling NAN and
sign tracking. And that will likely be after Cauldron because it will need
further testing (lapack, ppc64le, -ffinite-math-only, etc).
Regstrapped on x86-64 Linux, plus I ran selftests for
-ffinite-math-only.
gcc/ChangeLog:
* range-op-float.cc (frange_add_zeros): New.
(build_le): Call frange_add_zeros.
(build_ge): Same.
(foperator_equal::op1_range): Same.
(foperator_not_equal::op1_range): Same.