gcc8 is too old for std::for_each_n

Index: alc/alu.cpp
--- alc/alu.cpp.orig
+++ alc/alu.cpp
@@ -2155,7 +2155,9 @@ void Write(const al::span<const FloatBufferLine> InBuf
             out[c] = SampleConv<T>(s);
             out += ptrdiff_t(FrameStep);
         };
-        std::for_each_n(inbuf.cbegin(), SamplesToDo, conv_sample);
+        auto first = inbuf.cbegin();
+        auto last = first + SamplesToDo;
+        std::for_each(first, last, conv_sample);
         ++c;
     }
     if(const size_t extra{FrameStep - c})
