Warn projects not to use it because PUBLIC_LIBRARIES don't make
sense for executable targets and it also led to some issues in the
internal functions where some of them did not expect to receive
PUBLIC_LIBRARIES.
To ensure builds don't needlessly break, treat PUBLIC_LIBRARIES values
as regular LIBRARIES. In the future we might add an error instead.
Using PUBLIC_LIBRARIES in qt_internal_add_app, etc, accidentally
worked because the option name and the values following it were
parsed as values of the "previous" option, like SOURCES or
INCLUDE_DIRECTORIES or LIBRARIES, and when those got
passed through to qt_internal_extend_target, things magically worked.
We have a lot of projects using PUBLIC_LIBRARIES, mostly due to the
way qmake pro files were written and how pro2cmake converted them.
We'll have to clean up each repo.
Change-Id: I69e09d34afdf98f0d47c08d324643fc986f8131c
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
ea8645d846