Description:

Failed to build from source (version: 0.3.0-1) on RISC-V64 machine. This is the error message:

```
error: failed to run custom build command for `mitmproxy v0.3.0 (/build/python-mitmproxy-rs/src/mitmproxy_rs-0.3.0)`

Caused by:
process didn't exit successfully: `/build/python-mitmproxy-rs/src/mitmproxy_rs-0.3.0/target/release/build/mitmproxy-3b069f1b75be182d/build-script-build` (exit status: 101)
--- stderr
thread 'main' panicked at 'protoc is not available: Error { os: "linux", arch: "riscv64" }', build.rs:6:53
```

If the `PROTOC` environment variable is set during the build process, this package will use the `protoc` binary in the `PROTOC` path. Otherwise, it will use the packaged `protoc` binary in `protoc_bin_vendored`. Source Code: https://github.com/mitmproxy/mitmproxy_rs/blob/e81d487f0f64d1ee9a6e1cf3f4e77dc0d266e445/build.rs

While this problem can be solved by adding the binaries under the corresponding platforms to `protoc_bin_vendored`, we believe that a more reasonable way is to modify the PKGBUILD:

```
- makedepends=('maturin' 'python-installer' 'cargo')
+ makedepends=('maturin' 'python-installer' 'cargo' 'protobuf')

build() {
+ export PROTOC=$(command -v protoc)
}
```

You can also find the solution here: https://github.com/felixonmars/archriscv-packages/pull/3043