CMake: Make benchmark buildable standalone


Add the necessary project file stanza that allows to configure the
benchmarks with qt-cmake-private.

Change-Id: I51394344e801d43932d3691e654217cfed6336fc
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
commitc8e7ad34998b5adf4a099b3c48eb8b6969d7961f
parentf9e86518c548d54d7469b8bb68b1cfd1501f550b
authorJoerg Bornemann <joerg.bornemann@qt.io>
committerJoerg Bornemann <joerg.bornemann@qt.io>
commit timeWed, 30 Sep 2026 13:33:40 +0000