newlib: skip locking when within the NMI Irq.
newlib: skip locking when within the NMI Irq.

NMI Irq error paths call into printf which will use the newlib locks
but these can not be used within the NMI, a task switch can not occur
here. This case would be a terminal error path that is attempting to
write some debug message in the process, so just bail out of the
locking in this case. As a warning a ':' character is emitted and this
will typically prefix lines emitted in this context - it would be an
error for this path to be take in normal operation.

ourairquality/esp-open-rtos,ourairquality/esp-open-rtos,ourairquality/esp-open-rtos,ourairquality/esp-open-rtos,ourairquality/esp-open-rtos,ourairquality/esp-open-rtos