loader: make sure Go version is plumbed through

This fixes the new loop variable behavior in Go 1.22.

Specifically:
  * The compiler (actually, the x/tools/go/ssa package) now correctly
    picks up the Go version.
  * If a module doesn't specify the Go version, the current Go version
    (from the `go` tool and standard library) is used. This fixes
    `go run`.
  * The tests in testdata/ that use a separate directory are now
    actually run in that directory. This makes it possible to use a
    go.mod file there.
  * There is a test to make sure old Go modules still work with the old
    Go behavior, even on a newer Go version.

compileopts/options.go

@@ -23,6 +23,7 @@ type Options struct {
 	GOOS            string // environment variable
 	GOARCH          string // environment variable
 	GOARM           string // environment variable (only used with GOARCH=arm)
+	Directory       string // working dir, leave it unset to use the current working dir
 	Target          string
 	Opt             string
 	GC              string
@@ -48,7 +49,6 @@ type Options struct {
 	Programmer      string
 	OpenOCDCommands []string
 	LLVMFeatures    string
-	Directory       string
 	PrintJSON       bool
 	Monitor         bool
 	BaudRate        int