zgeru(3) on Linux

The text e6f4b142d4b8, as Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze), Debian 5.0 (Lenny), Debian 4.0 (Etch) shipped it.

perform the rank 1 operation A := alpha*x*y' + A,