Go project using go-keychain fails with GOOS=linux

I was trying to build some tooling using keybase/go-keychain to interact with keychain, since the README seemed to indicate that it also worked in Linux (I assumed that it was with a system keyring).

However, when trying to build my project on my mac I get the following.
I'm pretty new to the Go world, I apologise if this is something really dummy.

Go 1.23.6
MacOS 15.3.1 / Darwin 24.3

```
❯ CGO_ENABLED=1 GOOS=linux GOARCH=arm64 go build -v ./...
runtime/cgo
# runtime/cgo
linux_syscall.c:67:13: error: call to undeclared function 'setresgid'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
linux_syscall.c:67:13: note: did you mean 'setregid'?
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/unistd.h:593:6: note: 'setregid' declared here
linux_syscall.c:73:13: error: call to undeclared function 'setresuid'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
linux_syscall.c:73:13: note: did you mean 'setreuid'?
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/unistd.h:595:6: note: 'setreuid' declared here
```

Start by reproducing the reported GOOS=linux GOARCH=arm64 build command and compare its behavior with the Linux support described in the go-keychain README. Inspect the runtime/cgo/linux_syscall.c references and the macOS SDK unistd.h declarations. Done means establishing whether this cross-build is supported and documenting or resolving the reported failure.

Written by the indexing model from the issue text.