[Go] Doesn't build on riscv64-freebsd

[clausecker]

Describe the bug, including details regarding any error messages, version, and platform.

While building a project (github.com/brimdata/zed/cmd/zed) on riscv64-freebsd, we encountered a build failure in this project:

# github.com/apache/arrow/go/v11/internal/utils
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:76:4: undefined: TransposeInt8Int8
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:78:4: undefined: TransposeInt8Int16
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:80:4: undefined: TransposeInt8Int32
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:82:4: undefined: TransposeInt8Int64
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:84:4: undefined: TransposeInt8Uint8
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:86:4: undefined: TransposeInt8Uint16
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:88:4: undefined: TransposeInt8Uint32
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:90:4: undefined: TransposeInt8Uint64
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:95:4: undefined: TransposeInt16Int8
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:97:4: undefined: TransposeInt16Int16
vendor/github.com/apache/arrow/go/v11/internal/utils/transpose_ints_def.go:97:4: too many errors

It appears that support code for riscv64 is missing. Please add such code.

Component(s)

Go

[zeroshade]

This is definitely an oversight in the way I implemented it. I'll fix this up so that it should properly default to the pure go impls for anything that we don't have a specific implementation for. That way future platform additions like go1.20 adding riscv64 won't break. I'll get this in quickly so it can make it into v12.

[clausecker]

Thanks, that would be great!