CMake: Make benchmarks buildable standalone


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

Change-Id: If2ea7e600d4d79dd79e16285218fb5f00f874fd4
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
commitc750387f1d82606235b0fbdc6b69f23a8347d35f
parentf08a6df17433e390b442465648c76040b0049e12
authorJoerg Bornemann <joerg.bornemann@qt.io>
committerJoerg Bornemann <joerg.bornemann@qt.io>
commit timeWed, 30 Sep 2026 13:34:08 +0000