protobuf v1.28.1 compile issue + missing MapOf in reflect

[abourget]

With tinygo's dev branch (commit 0566bbf), compiling google.golang.org/protobuf v1.28.1 I get:

$ /Users/abourget/dev/tinygo/build/tinygo build -scheduler=none -o eth_xfer.wasm -target wasi eth_xfer.go
# google.golang.org/grpc/internal/channelz
../../../../../go/pkg/mod/google.golang.org/grpc@v1.51.0/internal/channelz/types_linux.go:39:54: SOL_SOCKET not declared by package syscall
../../../../../go/pkg/mod/google.golang.org/grpc@v1.51.0/internal/channelz/types_linux.go:39:74: SO_LINGER not declared by package syscall
../../../../../go/pkg/mod/google.golang.org/grpc@v1.51.0/internal/channelz/types_linux.go:42:55: SOL_SOCKET not declared by package syscall
../../../../../go/pkg/mod/google.golang.org/grpc@v1.51.0/internal/channelz/types_linux.go:42:75: SO_RCVTIMEO not declared by package syscall
../../../../../go/pkg/mod/google.golang.org/grpc@v1.51.0/internal/channelz/types_linux.go:45:55: SOL_SOCKET not declared by package syscall
../../../../../go/pkg/mod/google.golang.org/grpc@v1.51.0/internal/channelz/types_linux.go:45:75: SO_SNDTIMEO not declared by package syscall
../../../../../go/pkg/mod/google.golang.org/grpc@v1.51.0/internal/channelz/types_linux.go:48:55: SOL_TCP not declared by package syscall
../../../../../go/pkg/mod/google.golang.org/grpc@v1.51.0/internal/channelz/types_linux.go:48:72: TCP_INFO not declared by package syscall

Been trying to chase the compilation issue, and there's always something creeping back in.

Prior to this, I had an issue with MapOf and added:

func MapOf(key, elem Type) Type {
    panic("not implemented in tinygo")
}

to src/reflect/type.go, to not get:

# github.com/golang/protobuf/proto
../../../../../go/pkg/mod/github.com/golang/protobuf@v1.5.2/proto/registry.go:224:16: MapOf not declared by package reflect

I'm running on go version go1.19.4 darwin/arm64.

Relates to #2667