gitlab-ci: restore lto testing on OSX

Found that after commit:

  7faa1abe "gitlab-ci: implement OSX 10.14 testing on mac mini"

the variable environment CMAKE_EXTRA_PARAMS, which turns on LTO flag
on OSX compilation was mistakenly missed to be updated and LTO feature
was disabled on OSX testing in real. After it some later commits
generated the missed LTO errors, which the current commit fixed.

Closes #5160