syscall: hide internal comment from Syscall documentation

There's a comment on the Syscall function that's supposed to be an
internal implementation note, but since it's not separated from the
function definition, it appears in godoc. Add a blank line to prevent
this.

Change-Id: Iba307f1cc3844689ec3c6d82c21d441852e35bca
Reviewed-on: https://go-review.googlesource.com/c/go/+/236561
Reviewed-by: Brad Fitzpatrick <[email protected]>

src/syscall/dll_windows.go

@@ -21,6 +21,7 @@ type DLLError struct {
 func (e *DLLError) Error() string { return e.Msg }
 
 // Implemented in ../runtime/syscall_windows.go.
+
 func Syscall(trap, nargs, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
 func Syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
 func Syscall9(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno)