mwg/std/cmath: add isunordered, is{greater,less}{,equal}, islessgreater
mwg/std/cmath: add isunordered, is{greater,less}{,equal}, islessgreater

akinomyoga/libmwg,akinomyoga/libmwg,akinomyoga/libmwg,akinomyoga/libmwg,akinomyoga/libmwg