what GCC for dhrystone?

[AnttiLukats]

rules say in "min requirements" that zephyr app compiled with unmodified GCC from zephyr should be used, but the rules do not say the core may not be usable with other compilers. So very strictly the rules do not specify the compiler for dhrystone, only that -O -fno_inline should be used.

RECOMMENDATION: use mainline unmodified GCC version, if possible without recompiling it from sources.