Add constexpr hashlib default constructors

Signed-off-by: Claire Xenia Wolf <claire@clairexen.net>

kernel/hashlib.h

@@ -420,7 +420,7 @@ public:
 		operator const_iterator() const { return const_iterator(ptr, index); }
 	};
 
-	dict()
+	constexpr dict()
 	{
 	}
 
@@ -855,7 +855,7 @@ public:
 		operator const_iterator() const { return const_iterator(ptr, index); }
 	};
 
-	pool()
+	constexpr pool()
 	{
 	}
 
@@ -1062,6 +1062,10 @@ public:
 		const K *operator->() const { return &container[index]; }
 	};
 
+	constexpr idict()
+	{
+	}
+
 	int operator()(const K &key)
 	{
 		int hash = database.do_hash(key);
@@ -1132,6 +1136,10 @@ class mfp
 public:
 	typedef typename idict<K, 0, OPS>::const_iterator const_iterator;
 
+	constexpr mfp()
+	{
+	}
+
 	int operator()(const K &key) const
 	{
 		int i = database(key);