Add code to find luprex root directory

luprex/cpp/drv/drvutil.hpp

@@ -15,6 +15,7 @@
 #include <ostream>
 #include <sstream>
 #include <algorithm>
+#include <filesystem>
 
 namespace drvutil {
 
@@ -37,7 +38,7 @@ namespace drvutil {
 // returns an error message.  In this case, the ostream contains garbage.  If
 // there is no error, returns the empty string.
 //
-std::string package_lua_source(const std::string &base, std::ostream *oss);
+std::string package_lua_source(const std::filesystem::path &base, std::ostream *oss);
 
 // Parse a target designation.
 //