copy these two folders to
install feeds from openwrt official package repository.
./scripts/feeds update -a ./scripts/feeds install -a
use 'make menuconfig' to select trojan package
the buildroot generate trojan binary linked to our openssl. You may use 'make package/trojan/{clean,compile} V=99' or whatever you like.
edit '/etc/config/trojan' file to enable it. The init script is disabled by default to avoid startup before configuration.
Q: May I use openssl from openwrt? A: As long as you don't need cutting-edge features, e.g. TLS 1.3. BTW, the Makefile doesn't depend on official openssl package.