CMake: Make benchmarks buildable standalone


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

Change-Id: If038df0d38ef1ad57fd6739bba820df6f6ecd8c2
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
commita9ee2c8d209d1becddf250321c95c0b512998701
parentb20fe1b3db702f8e6dd3f2d5f486cdb42a01a707
authorJoerg Bornemann <joerg.bornemann@qt.io>
committerJoerg Bornemann <joerg.bornemann@qt.io>
commit timeWed, 30 Sep 2026 13:33:49 +0000