Starting a new Slicer instance from the menu - fix of Windows build

src/slic3r/GUI/MainFrame.cpp

@@ -13,7 +13,6 @@
 #include <wx/debug.h>
 
 #include <boost/algorithm/string/predicate.hpp>
-#include <boost/process/spawn.hpp>
 
 #include "libslic3r/Print.hpp"
 #include "libslic3r/Polygon.hpp"
@@ -41,6 +40,12 @@
 #include <shlobj.h>
 #endif // _WIN32
 
+// For starting another PrusaSlicer instance on OSX.
+// Fails to compile on Windows on the build server.
+#ifdef __APPLE__
+    #include <boost/process/spawn.hpp>
+#endif
+
 namespace Slic3r {
 namespace GUI {