Add the Whetstone floating-point benchmark to NuttX applications.
The Whetstone benchmark is a widely-used tool for evaluating FPU
(floating-point unit) performance.
This benchmark is ported from netlib.org whetstone.c which has a
custom permissive license requiring attribution. Therefore it
depends on ALLOW_CUSTOM_PERMISSIVE_COMPONENTS.
Usage: whetstone [loops]
Signed-off-by: makejian <makejian@xiaomi.com>
