Wrong rust-lld used for target riscv64gc-unknown-linux-gnu

  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: rust-lld: error: /tmp/rustccLx4WH/symbols.o is incompatible with elf64-x86-64
          rust-lld: error: /root/github/rusty-rain/target/riscv64gc-unknown-linux-gnu/release/deps/rusty_rain-f9cdb814e0fff0bf.rusty_rain.d9a7a1be04eb8039-cgu.00.rcgu.o is incompatible with elf64-x86-64

I think it's an evident fact according to the log above.

And I've tried to use a custom linker but failed.

[target.riscv64gc-unknown-linux-gnu]
cc = "riscv64-linux-gnu-gcc"
cxx = "riscv64-linux-gnu-g++"
ar = "riscv64-linux-gnu-ar"
ranlib = "riscv64-linux-gnu-ranlib"
linker = "riscv64-linux-gnu-gcc"

[env]
CC_riscv64gc-unknown-linux-gnu="riscv64-linux-gnu-gcc"
CXX_riscv64gc-unknown-linux-gnu="riscv64-linux-gnu-g++"
AR_riscv64gc-unknown-linux-gnu="riscv64-linux-gnu-ar"
RANLIB_riscv64gc-unknown-linux-gnu="riscv64-linux-gnu-ranlib"
LINKER_riscv64gc-unknown-linux-gnu="riscv64-linux-gnu-gcc"

error: expected a table, but found a string for `target.riscv64gc-unknown-linux-gnu.ranlib` in /root/github/rusty-rain/.cargo/config.toml

Start with the reported .cargo/config.toml target.riscv64gc-unknown-linux-gnu table and reproduce the build with Cargo's verbose linker arguments. Investigate why rust-lld is selected despite the configured linker and why the ranlib value is parsed as a string. Done means the target build selects a compatible RISC-V linker without the reported ELF incompatibility.