hecl/hecl: Remove windows ifdef in CaseInsensitiveCompare

This is technically still usable for non-Windows systems, given there's
nothing directly Windows-specific about the operator overload

hecl/include/hecl/hecl.hpp

@@ -503,13 +503,11 @@ struct CaseInsensitiveCompare {
     });
   }
 
-#if _WIN32
   bool operator()(std::wstring_view lhs, std::wstring_view rhs) const {
     return std::lexicographical_compare(lhs.begin(), lhs.end(), rhs.begin(), rhs.end(), [](wchar_t lhs, wchar_t rhs) {
       return std::towlower(lhs) < std::towlower(rhs);
     });
   }
-#endif
 };
 
 /**