`(abs -0.0)` yields `-0.0` on several implementations

[okuoku]

As mentioned in SIBR0013 document, several implementations return minus value with abs if argument was -0.0.

    # (abs -0.0) => -0.0
    inexact3-CHIBI_SCHEME
    inexact3-DIGAMMA
    inexact3-FOMENT
    inexact3-KAWA
    inexact3-STKLOS

Even on these implementations, (atan -0.0 1.0) is -0.0 thus we know they can handle -0.0 during computation.

It might be better to check truncation as well: shirok/Gauche@ca136f1#diff-84296dbbce35929ab06ca6deb1cac5abde4d8a0f896b2657491432061ca92e37R1839-R1841