ci: build samples/cpp/hello_world as part of the multiplatform test

Build the C++ version of the Hello, World sample as part of the
multiplatform (build) test in CI.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>
(cherry picked from commit cd543887f41af8fcf504dded51f2346b605731d5)
1 file changed