Add portYIELD_FROM_ISR() macros to Cortex-M ports. The new macro just calls the exiting portEND_SWITCHING_ISR() macro.
Remove code from the MSVC port layer that was left over from a previous implementation and become obsolete.
Replaced the #error that traps configMAX_SYSCALL_INTERRUPT_PRIORITY being set to 0 with a configASSERT() for GCC Cortex-M3/4 ports as the #error does not work if configMAX_SYSCALL_INTERRUPT_PRIORITY includes any casting. Not a problem for other compilers as they cannot have casting anyway as that would break the assembly code.
Richard Barry