Clean up the CMake configuration by removing the obsolete
`BUILD_OOTCPP` guard. This variable is no longer required
since out-of-tree build handling is now managed via the
enhanced `nuttx_add_subdirectory()` with EXCLUDE support.
* Simplifies CMake configuration command.
* Avoids redundant or unused build options.
Signed-off-by: trns1997 <trns1997@gmail.com>
Introduce a new CI test to validate out-of-tree builds
and prevent regressions in the `make export` workflow.
Specifically, this change adds `test-oot-build.sh` that:
* Builds NuttX using a selected configuration.
* Runs `make export` to generate the export package.
* Copies the `nuttx-export` to the OOT build project.
* Verifies that compilation and linking succeed.
Signed-off-by: trns1997 <trns1997@gmail.com>