Modify cpp-use-cases.md to fix build_file
Modify cpp-use-cases.md to fix build_file

The build_file parameter for `gtest.BUILD` after the `strip_prefix` process was wrongly configured without the preceding `@//:`, which leads it to not discover the `gtest.BUILD` file and thus fail the build

Resolves #9312

Closes #9313.

PiperOrigin-RevId: 266965310

werkt/bazel,perezd/bazel,ButterflyNetwork/bazel,ulfjack/bazel,bazelbuild/bazel,twitter-forks/bazel,ulfjack/bazel,davidzchen/bazel,werkt/bazel,katre/bazel,dslomov/bazel-windows,aehlig/bazel,davidzchen/bazel,akira-baruah/bazel,twitter-forks/bazel,davidzchen/bazel,akira-baruah/bazel,dslomov/bazel-windows,dslomov/bazel,ButterflyNetwork/bazel,ulfjack/bazel,safarmer/bazel,aehlig/bazel,meteorcloudy/bazel,meteorcloudy/bazel,werkt/bazel,cushon/bazel,twitter-forks/bazel,dslomov/bazel,ButterflyNetwork/bazel,cushon/bazel,dslomov/bazel,ulfjack/bazel,safarmer/bazel,bazelbuild/bazel,meteorcloudy/bazel,ButterflyNetwork/bazel,dslomov/bazel-windows,cushon/bazel,katre/bazel,aehlig/bazel,akira-baruah/bazel,dslomov/bazel,akira-baruah/bazel,perezd/bazel,perezd/bazel,dslomov/bazel,twitter-forks/bazel,dslomov/bazel-windows,aehlig/bazel,meteorcloudy/bazel,katre/bazel,perezd/bazel,dslomov/bazel,cushon/bazel,ButterflyNetwork/bazel,aehlig/bazel,twitter-forks/bazel,bazelbuild/bazel,ulfjack/bazel,cushon/bazel,ButterflyNetwork/bazel,davidzchen/bazel,twitter-forks/bazel,bazelbuild/bazel,bazelbuild/bazel,aehlig/bazel,akira-baruah/bazel,ulfjack/bazel,safarmer/bazel,meteorcloudy/bazel,meteorcloudy/bazel,bazelbuild/bazel,katre/bazel,dslomov/bazel,aehlig/bazel,davidzchen/bazel,cushon/bazel,safarmer/bazel,ulfjack/bazel,meteorcloudy/bazel,perezd/bazel,dslomov/bazel-windows,safarmer/bazel,werkt/bazel,davidzchen/bazel,davidzchen/bazel,dslomov/bazel-windows,katre/bazel,akira-baruah/bazel,perezd/bazel,katre/bazel,werkt/bazel,twitter-forks/bazel,werkt/bazel,perezd/bazel,safarmer/bazel