I just created a project for the stm32f0-discovery board including FreeRTOS and building with OpenSTM32/eclipse. The path to cmsis_os.h was missing and easily fixed by adding "Middlewares/Third_Party/FreeRTOS/Source/CMSIS_RTOS" to the include paths. I have attached the .IOC file for your viewing pleasure. (Apologies for misnaming it - it should have been myMX19proj but it seems that once saved, it cannot be changed.)
Thank you for your continuing support of Cube on Linux.