use ADL lookup for erase_if instead of adding to std (gtl reported issue)

parallel_hashmap/phmap.h

@@ -3335,6 +3335,7 @@ public:
     //   flat_hash_set<std::string> s;
     //   // Uses "abc" directly without copying it into std::string.
     //   s.erase("abc");
+    //
     // --------------------------------------------------------------------
     template <class K = key_type>
     size_type erase(const key_arg<K>& key) {
@@ -3366,15 +3367,22 @@ public:
     //     ++it;
     //   }
     // }
+    //
+    // Do not use erase APIs taking iterators when accessing the map concurrently
     // --------------------------------------------------------------------
-    void _erase(iterator it) {
-        assert(it.inner_ != nullptr);
-        it.inner_->set_._erase(it.it_);
+    void _erase(iterator it, bool do_lock = true) {
+        Inner* inner = it.inner_;
+        assert(inner != nullptr);
+        auto&  set   = inner->set_;
+        // typename Lockable::UniqueLock m(*inner); // don't lock here 
+        
+        set._erase(it.it_);
     }
     void _erase(const_iterator cit) { _erase(cit.iter_); }
 
     // This overload is necessary because otherwise erase<K>(const K&) would be
     // a better match if non-const iterator is passed as an argument.
+    // Do not use erase APIs taking iterators when accessing the map concurrently
     // --------------------------------------------------------------------
     iterator erase(iterator it) { _erase(it++); return it; }
 
@@ -3387,6 +3395,7 @@ public:
 
     // Moves elements from `src` into `this`.
     // If the element already exists in `this`, it is left unmodified in `src`.
+    // Do not use erase APIs taking iterators when accessing the map concurrently
     // --------------------------------------------------------------------
     template <typename E = Eq>
     void merge(parallel_hash_set<N, RefSet, Mtx_, Policy, Hash, E, Alloc>& src) {  // NOLINT
@@ -4992,9 +5001,6 @@ namespace phmap {
             return old_size - c.size();
         }
     } // priv
-} // phmap
-
-namespace std {
 
     // ======== erase_if for phmap set containers ==================================
     template <class T, class Hash, class Eq, class Alloc, class Pred> 
@@ -5038,7 +5044,7 @@ namespace std {
         return phmap::priv::erase_if(c, std::move(pred));
     }
 
-} // std
+} // phmap
 
 #ifdef _MSC_VER
      #pragma warning(pop)