CMake: Make benchmarks buildable standalone


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

Change-Id: I13b6ecaf26e684414b1f39103a6cb657f58dfd81
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
commiteba122c652a90af16c075e9e1fa173ca76723726
parent5273c7c73b1eede8a46031d4bef7f1f3d6a88d7a
authorJoerg Bornemann <joerg.bornemann@qt.io>
committerJoerg Bornemann <joerg.bornemann@qt.io>
commit timeWed, 30 Sep 2026 13:33:55 +0000