Fixes for Boost compatibility.
This patch comes from Gentoo:
 portage/media-gfx/prusaslicer/files/prusaslicer-2.5.0_alpha2-boost-fixes.patch

--- a/src/hints/HintsToPot.cpp
+++ b/src/hints/HintsToPot.cpp
@@ -1,6 +1,7 @@
 #include <iostream>
 #include <vector>
 #include <string>
+#include <boost/nowide/fstream.hpp>
 #include <boost/filesystem.hpp>
 #include <boost/dll.hpp>
 #include <boost/property_tree/ini_parser.hpp>
@@ -9,7 +10,7 @@
 
 bool write_to_pot(boost::filesystem::path path, const std::vector<std::pair<std::string, std::string>>& data)
 {
-	boost::filesystem::ofstream file(std::move(path), std::ios_base::app);
+	boost::nowide::ofstream file(std::move(path), std::ios_base::app);
 	for (const auto& element : data)
 	{
 		//Example of .pot element 
--- a/src/libslic3r/Preset.cpp
+++ b/src/libslic3r/Preset.cpp
@@ -25,6 +25,7 @@
 #include <stdexcept>
 #include <unordered_map>
 #include <boost/format.hpp>
+#include <boost/nowide/fstream.hpp>
 #include <boost/filesystem.hpp>
 #include <boost/filesystem/fstream.hpp>
 #include <boost/algorithm/string.hpp>
@@ -84,7 +85,7 @@ ConfigFi</td></tr></table>
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