Fix last modified for long paths on windows

It is necessary to prefix the file name passed into CreateFile with
"\\?\" to allow file names with more than max_path (260) characters on
windows:
https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea..

Fixes sbt/sbt#5098.

io/src/main/scala/sbt/internal/io/Milli.scala

@@ -263,7 +263,7 @@ private object WinMilli extends MilliNative[FILETIME] {
 
   private def getHandle(lpFileName: String, dwDesiredAccess: Int, dwShareMode: Int): HANDLE = {
     val hFile = CreateFile(
-      lpFileName,
+      "\\\\?\\" + lpFileName,
       dwDesiredAccess,
       dwShareMode,
       null,

io/src/test/scala/sbt/io/LastModifiedSpec.scala

@@ -0,0 +1,31 @@
+/*
+ * sbt IO
+ *
+ * Copyright 2011 - 2019, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ *
+ * Licensed under Apache License 2.0
+ * (http://www.apache.org/licenses/LICENSE-2.0).
+ */
+
+package sbt.io
+
+import java.nio.file.Files
+
+import org.scalatest.FlatSpec
+
+class LastModifiedSpec extends FlatSpec {
+  "IO.getModifiedTimeOrZero" should "work with long path names" in IO.withTemporaryDirectory {
+    dir =>
+      val fileName = "a" * 32
+      val nested =
+        (1 to 8).foldLeft(dir.toPath) {
+          case (d, _) => Files.createDirectories(d.resolve(fileName))
+        }
+      val file = Files.createFile(nested.resolve(fileName)).toFile
+      // in case target platform only has second precision round to nearest second
+      val lm = (System.currentTimeMillis / 1000) * 1000
+      IO.setModifiedTimeOrFalse(file, lm)
+      assert(IO.getModifiedTimeOrZero(file) == lm)
+  }
+}