Automatically detect native endianness for IAR compiler platform. (#612)
* Auto detect native endianness for IAR compiler platform.
References:
- [IAR C/C++ Development Guide Compiling and Linking for Arm Limited’s **Arm**® Cores](https://wwwfiles.iar.com/arm/webic/doc/ewarm_developmentguide.enu.pdf)
- [IAR C/C++ Compiler User Guide for Microchip Technology’s **AVR** Microcontroller Family](https://wwwfiles.iar.com/AVR/webic/doc/EWAVR_CompilerGuide.pdf)
* Fix spelling mistake.
