handshake: get rid of stpcpy
handshake: get rid of stpcpy

stpcpy was added in POSIX.1-2008 and is not present on some systems like
Android.

rlei/fastd-android,rlei/fastd-android,fpletz/fastd,rlei/fastd-android,fpletz/fastd,fpletz/fastd,rlei/fastd-android,fpletz/fastd,fpletz/fastd,rlei/fastd-android