CMake: allow configuring target architecture
Default to -march=native, unless we detect cross-compiling, in which
case default to leaving out -march=... entirely (as detecting the host
system's architecture doesn't help with optimizing for the target
CMake: don't auto-run tests if cross-compiling
Otherwise this could fail if, say, you're building for an ARM system
from an x86 system.
Add CMake build system support
Make conversions explicit in x25519.h
Clear "potential loss of data" warnings from MSVC.
Disable system dialog when tests fail on Windows
Remove unnecessary ../ from includes
Add support for nRF52832 boards using HW RNG
Tested on an Adafruit Feather nRF52832.
Remove unused variables from copy/pasted RNG code