Removed these cargo unstable features:

`-Zbuild-std=core,alloc -Zbuild-std-features=compiler-builtins-mem`

Add some libc function

update build&run C apps info in README.md

Add support of x86_64

Finish Completely Fair Scheduler and APP Priority

it's allow to use `info!()` in `axhal::platform_init()`

See https://github.com/rust-lang/rust/pull/109507

Add udp and dns support 添加udp和dns支持