In your image.bb add:

TOOLCHAIN_HOST_TASK:append = " openssl"

This is rather implicitly suggested by the docs as well.

Take note:

• Space before openssl: " openssl".
• The TOOLCHAIN_HOST_TASK variable can only be changed from the image you build the SDK for or in your config, e.g. local.conf.

If this doesn't fix it, please provide more information, like the exact lines that you tried.