Alloc sync support target_has_atomic no ptr

[zhang-wenchao]

Building error:

| #[auto_impl::auto_impl(&, Arc)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ could not find `sync` in `alloc`
    |
note: found an item that was configured out
   --> /home/life/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/lib.rs:229:9
    |
229 | pub mod sync;
    |         ^^^^
note: the item is gated here
   --> /home/life/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/lib.rs:228:1
    |
228 | #[cfg(all(not(no_rc), not(no_sync), target_has_atomic = "ptr"))]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: this error originates in the attribute macro `auto_impl::auto_impl` (in Nightly builds, run with -Z macro-backtrace for more info)

Target riscv32i-unknown-none-elf