Fix Linux build.

syscall_linux.go

@@ -0,0 +1,16 @@
+package bolt
+
+import (
+	"syscall"
+)
+
+type _syscall interface {
+	Mmap(fd int, offset int64, length int, prot int, flags int) (data []byte, err error)
+}
+
+type syssyscall struct{}
+
+func (o *syssyscall) Mmap(fd int, offset int64, length int, prot int, flags int) (data []byte, err error) {
+	// err = (EACCES, EBADF, EINVAL, ENODEV, ENOMEM, ENXIO, EOVERFLOW)
+	return syscall.Mmap(fd, offset, length, prot, flags)
+}

syscall_linux_test.go

@@ -0,0 +1,14 @@
+package bolt
+
+import (
+	"github.com/stretchr/testify/mock"
+)
+
+type mocksyscall struct {
+	mock.Mock
+}
+
+func (m *mocksyscall) Mmap(fd int, offset int64, length int, prot int, flags int) (data []byte, err error) {
+	args := m.Called(fd, offset, length, prot, flags)
+	return args.Get(0).([]byte), args.Error(1)
+}