emyg_atod: Use scalbn(C99) instead of scalb
emyg_atod: Use scalbn(C99) instead of scalb

scalb() was removed in POSIX 2008. It is not implemented in
Cygwin(newlib).

dcurrie/picrin,picrin-scheme/picrin,picrin-scheme/picrin,omasanori/picrin,omasanori/picrin,dcurrie/picrin