* Simplify EINTR/ECANCEL error handling
1. Add semaphore uninterruptible wait function
2 .Replace semaphore wait loop with a single uninterruptible wait
3. Replace all sem_xxx to nxsem_xxx
* Unify the void cast usage
1. Remove void cast for function because many place ignore the returned value witout cast
2. Replace void cast for variable with UNUSED macro
Squashed commit of the following:
configs/viewtool-stm32f107: Clean up some compilation errors. Now all builds correctly and is ready for test.
arch/arm/src/stm32: Do not condition building STM32 USB host logic on CONFIG_USBHOST. That then precludes building STM32 platforms with external USB host chips like the MAX3421E. Add an new, STM32-internal variable CONFIG_STM32_USBHOST that does the same job without such side-effects.
configs/viewtool-stm32f107: Add support for MAX3421E USB host.
