Update to the latest atomic.h.

Update to the latest atomic.h.
Improve commenting in RISC-V GCC port.
Fix IAR RISC-V port so the first task starts with interrupts enabled.
Add references to third party page ref using newlib with FreeRTOS into the tasks.c file in each place newlib is referenced.
Move the position of the traceTASK_DELETE() trace macro in case of use with a memory allocator that writes over freed memory even when inside a critical section.
Efficiency improvement:  Make sure xTaskIncrementTick() does not return pdTRUE when the scheduler is locked.  This just prevents an unnecessary yield interrupt (unnecessary as it is ignored) when xYieldPending happens to be pdTRUE.

git-svn-id: https://svn.code.sf.net/p/freertos/code/trunk@2753 1d2547de-c912-0410-9cb9-b8ca96c0e9e2