cmd.Dir = w.context.Dir
		}
		cmd.Stderr = os.Stderr
		out, err := cmd.Output()
		if err != nil {
			log.Fatalf("loading imports: %v\n%s", err, out)
		}

		var stdPackages []string
		importMap := make(map[string]map[string]string)
		importDir := make(map[string]string)
		dec := json.NewDecoder(bytes.NewReader(out))
		for {
			var pkg struct {
				ImportPath, Dir string

	ErrInvalidUnreadRune = errors.New("bufio: invalid use of UnreadRune")
	ErrBufferFull        = errors.New("bufio: buffer full")
	ErrNegativeCount     = errors.New("bufio: negative count")
)

// Buffered input.

// Reader implements buffering for an io.Reader object.
type Reader struct {
	buf          []byte
	rd           io.Reader // reader provided by the client

a C source file for 6c; both compile as part of the named package
(gmp, in this example).  The third, gcc.c, is a C source file for gcc;
it compiles into a shared object (.so) that is dynamically linked into
any 6.out that imports the first two files.

The stanza

	// #include <gmp.h>
	import "C"

is a signal to cgo.  The doc comment on the import of "C" provides