extend stdlib to allow import of more packages (#1099)

* stdlib: extend stdlib to allow import of more packages

src/os/errors.go

@@ -0,0 +1,39 @@
+package os
+
+import (
+	"errors"
+)
+
+var (
+	ErrInvalid    = errors.New("invalid argument")
+	ErrPermission = errors.New("permission denied")
+	ErrClosed     = errors.New("file already closed")
+
+	// Portable analogs of some common system call errors.
+	// Note that these are exported for use in the Filesystem interface.
+	ErrUnsupported    = errors.New("operation not supported")
+	ErrNotImplemented = errors.New("operation not implemented")
+	ErrNotExist       = errors.New("file not found")
+	ErrExist          = errors.New("file exists")
+)
+
+func IsPermission(err error) bool {
+	return err == ErrPermission
+}
+
+func NewSyscallError(syscall string, err error) error {
+	if err == nil {
+		return nil
+	}
+	return &SyscallError{syscall, err}
+}
+
+// SyscallError records an error from a specific system call.
+type SyscallError struct {
+	Syscall string
+	Err     error
+}
+
+func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err.Error() }
+
+func (e *SyscallError) Unwrap() error { return e.Err }