include the platform header where Win32 types are used

windows.cpp and piped_proc.cpp reached windows.h through an imported
module's global module fragment, which does not cross the boundary.
LPT.cpp and zmq_input.cpp never had it at all - the first was in an
MSBuild batch that aborted before reaching it, the second is behind
WITH_ZMQ and has not been compiled by either CI job.

The earlier sweep only looked inside #ifdef _WIN32 blocks, but these
files are gated by CMake instead, so they have no such block.

extras/piped_proc.cpp

@@ -1,4 +1,7 @@
 module;
+#ifdef _WIN32
+#include "winheaders.h"   // the interface has this in its own fragment, which does not cross
+#endif
 #include <array>
 #include <chrono>
 #include <deque>