Demonstration of lld link error

Build the target using Rust 1.52.1 (stable) using the command:

rustup target add riscv32imac-unknown-none-elf
cargo build --target riscv32imac-unknown-none-elf

This will produce an error about "note: rust-lld: error: undefined symbol: __atomic_load_4"

Then, do one of the following:

• Comment out the syscall in src/main.rs
• Remove the rustflags from .cargo/config
• Build with riscv32i-unknown-none-elf
• Build with a previous version of Rust
• Modify Cargo.toml to use the bare-gdbstub repo instead of gdbstub

Any of these will resolve the error.