Add missing newline in OutputDebugStringA invocation.

Before this commit, every debug message was correctly printed
to stdout, but they were all concatenated onto a single line in
the Visual Studio "Output" pane.

src/platform/w32util.cpp

@@ -25,6 +25,7 @@ void dbp(const char *str, ...)
     // The native version of OutputDebugString, unlike most others,
     // is OutputDebugStringA.
     OutputDebugStringA(buf);
+    OutputDebugStringA("\n");
 
 #ifndef NDEBUG
     // Duplicate to stderr in debug builds, but not in release; this is slow.