idstring: Add 'in' function

Signed-off-by: gatecat <gatecat@ds0.me>

common/idstring.h

@@ -58,6 +58,16 @@ struct IdString
     bool empty() const { return index == 0; }
 
     unsigned int hash() const { return index; }
+
+    template <typename... Args> bool in(Args... args) const
+    {
+        // Credit: https://articles.emptycrate.com/2016/05/14/folds_in_cpp11_ish.html
+        bool result = false;
+        (void)std::initializer_list<int>{(result = result || in(args), 0)...};
+        return result;
+    }
+
+    bool in(const IdString &rhs) const { return *this == rhs; }
 };
 
 NEXTPNR_NAMESPACE_END