Enable supported bitmanip extensions for Rust demos

Ibex supports a few more bitmanip extensions but they're not supported
in upstream LLVM / Rust.

Author: jwnrt

sw/rust/.cargo/config.toml

@@ -5,6 +5,9 @@
 [build]
 target = "riscv32imc-unknown-none-elf"
 
+# Enable supported bitmanip extension features.
+rustflags = ["-Ctarget-feature=+zba,+zbb,+zbc,+zbs"]
+
 [target.riscv32imc-unknown-none-elf]
 runner = "../../util/load_demo_system.sh run"
 

sw/rust/rust-toolchain.toml

@@ -1,3 +1,3 @@
 [toolchain]
-targets = ["riscv32imc-unknown-none-elf"]
 channel = "nightly"
+components = ["rust-src"]