Misc Windows fixes.

(This is a merge of http://go/wvgerrit/70324)

- Add build settings for Windows.
- Conditionally add pthread.
- Add dummy DLLMain method.
- Fix #if checks for Windows.
- Remove designated initializers which aren't supported in MSVC.
- Remove variable length array.

Test: Android Unit Tests
Bug: 122953649
Change-Id: I14f16e7ce4b3ff17ee0139ea6c2f7243ae999aa1

libwvdrmengine/cdm/util/src/dllmain.cpp

@@ -0,0 +1,12 @@
+// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine Master
+// License Agreement.
+//
+// dllmain - A dummy DllMain method for Windows DLLs.
+//
+#include <windows.h>
+
+BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason,
+                    LPVOID lpReserved) {
+  return TRUE;
+}