Fixed C++20 ambiguous operator overload warning

src/usages_clang.cpp

@@ -27,7 +27,7 @@ std::map<boost::filesystem::path, Usages::Clang::Cache> Usages::Clang::caches;
 Mutex Usages::Clang::caches_mutex;
 std::atomic<size_t> Usages::Clang::cache_in_progress_count(0);
 
-bool Usages::Clang::Cache::Cursor::operator==(const Cursor &o) {
+bool Usages::Clang::Cache::Cursor::operator==(const Cursor &o) const {
   for(auto &usr : usrs) {
     if(clangmm::Cursor::is_similar_kind(o.kind, kind) && o.usrs.count(usr))
       return true;

src/usages_clang.hpp

@@ -64,7 +64,7 @@ namespace Usages {
         clangmm::Cursor::Kind kind;
         std::unordered_set<std::string> usrs;
 
-        bool operator==(const Cursor &o);
+        bool operator==(const Cursor &o) const;
       };
 
       class Token {