Several Makefiles: Add .PHONY definitions to prevent 'clean up to date' message weirdness; Add default definitions for some commonly used things when 'make clean' is used without .config or Make.defs files installed.

Add a simple test of the scheduler instrumentation logic.  This initial version is still kind of buggy.

apps/modbus/nuttx/portserial.c:  Was not returning an error on failure to open the device driver.  From Olololshka kokoko