Enable libdng_sdk for Windows

This is needed to use skia in Android Studio for Windows.
Changes include:
  - Replacing in dng_pthread.cpp '&operator(...) { }' with '&operator(...);'
to prevent 'control reaches end of non-void function' errors
  - Removing test of '_MSC_VER >= 1900' in dng_pthread.h as we use clang
for compilation which has a recent version of 'time.h' but fails the
test '_MSC_VER >= 1900'

Test: sdk build
Change-Id: I200d691378c5d3e7c1729b5f645766755aa3e296
diff --git a/Android.bp b/Android.bp
index 9299471..c7215e1 100644
--- a/Android.bp
+++ b/Android.bp
@@ -121,6 +121,17 @@
                 "-framework AppKit",
             ],
         },
+        windows: {
+            enabled: true,
+            cflags: [
+                "-D_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR",
+                "-Wno-null-arithmetic",
+                "-Wno-sign-compare",
+                "-Wno-tautological-pointer-compare",
+                "-Wno-unknown-pragmas",
+            ],
+            static_libs: ["libcompiler_rt-extras"],
+        },
     },
 
     export_include_dirs: ["source"],
diff --git a/source/dng_pthread.cpp b/source/dng_pthread.cpp
index 0347856..58c9ed0 100644
--- a/source/dng_pthread.cpp
+++ b/source/dng_pthread.cpp
@@ -75,7 +75,7 @@
 	void Lock()				   { ::EnterCriticalSection(&lock); }
 	void Unlock()			   { ::LeaveCriticalSection(&lock); }
 private:
-	dng_pthread_mutex_impl &operator=(const dng_pthread_mutex_impl &) { }
+	dng_pthread_mutex_impl &operator=(const dng_pthread_mutex_impl &);
 	dng_pthread_mutex_impl(const dng_pthread_mutex_impl &) { }
 };
 
@@ -95,7 +95,7 @@
 
 // Non copyable
 private:
-	dng_pthread_cond_impl &operator=(const dng_pthread_cond_impl &) { }
+	dng_pthread_cond_impl &operator=(const dng_pthread_cond_impl &);
 	dng_pthread_cond_impl(const dng_pthread_cond_impl &) { }
 
 };
@@ -122,7 +122,7 @@
 			mutex->Unlock();
 		}
 	private:
-		ScopedLock &operator=(const ScopedLock &) { }
+		ScopedLock &operator=(const ScopedLock &);
 		ScopedLock(const ScopedLock &) { }
 	};
 
diff --git a/source/dng_pthread.h b/source/dng_pthread.h
index 4572e31..80c3d24 100644
--- a/source/dng_pthread.h
+++ b/source/dng_pthread.h
@@ -53,18 +53,8 @@
 
 #endif
 
-// Use the standard "timespec" struct as "dng_timespec" for VS2015 and above
-// from <time.h>. Define "dng_timespec" as "timespec" otherwise.
-#if _MSC_VER >= 1900
 #include <time.h>
 #define dng_timespec timespec
-#else
-struct dng_timespec {
-	long tv_sec;
-	long tv_nsec;
-};
-#define timespec dng_timespec
-#endif
 
 #ifdef __cplusplus
 extern "C"