target-feature=-c doesn't disable zca feature on RISC-V

Code

I tried this code:

$(rustup which rustc --toolchain nightly) --target riscv32imac-unknown-none-elf -C target-feature=-c --print=cfg | grep target_feature

I expected to see this happen:
no target_feature="zca" in the output, because zca is the implied feature of "c".

Instead, this happened:
the output has target_feature="zca":

$(rustup which rustc --toolchain nightly) --target riscv32imac-unknown-none-elf -C target-feature=-c --print=cfg | grep target_feature
target_feature="a"
target_feature="m"
target_feature="zaamo"
target_feature="zalrsc"
target_feature="zca"

Version it worked on

It most recently worked on: Rust 1.90

Version with regression

$(rustup which rustc --toolchain 1.90) --target riscv32imac-unknown-none-elf -C target-feature=-c --print=cfg | grep target_feature
target_feature="a"
target_feature="m"

rustc --version --verbose:

rustc 1.90.0 (1159e78c4 2025-09-14)
binary: rustc
commit-hash: 1159e78c4747b02ef996e55082b704c09b970588
commit-date: 2025-09-14
host: aarch64-unknown-linux-gnu
release: 1.90.0
LLVM version: 20.1.8

Backtrace

<backtrace>

Start by running the provided rustc commands for riscv32imac-unknown-none-elf on the affected and working versions, then trace rustc's RISC-V target-feature handling. Check how disabling c affects the implied zca feature. Done means the affected command no longer reports target_feature="zca" while the other expected features remain unchanged, with regression coverage added.