On the minheadless VM that is built using cmake, the add_vm_plugin_sources cmake macro requires specifying the the plugin sources explicitly, which is omitting the src/plugins/SqueakSSL/SqueakSSL.c in the compilation of the plugin. By using the other macro (add_vm_plugin_auto), the platform specific files are automatically found with a glob pattern. This is a mistake that I introduced myself. This problem can be reproduced in Pharo using the minheadless vm of this repository on OS X with the following script:
´´´smalltalk url := 'https://google.com' asZnUrl. ZnClient new url: url; get; response ´´´
CI errors on travis are not related to this PR.