classq(3) on Linux

The text 10b069c506ee, as Debian 4.0 (Etch), Debian 3.1 (Sarge) shipped it.

return the values scl and ssq such that ( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,