resolves compilation error:	no member named 'multiplies' in namespace 'std' for library/src/twiddles.cpp

--- a/library/src/include/twiddles.h	2021-04-15 10:24:46.000000000 -0700
+++ b/library/src/include/twiddles.h	2021-07-21 22:27:10.760604147 -0700
@@ -9,6 +9,7 @@
 #include "../../../shared/gpubuf.h"
 #include "rocfft.h"
 #include <cassert>
+#include <functional>
 #include <math.h>
 #include <numeric>
 #include <tuple>