Add missing include for <algorithm>.

There is a change in llvm [1] that will soon don't automatically
surface symbols from a transitive include of <algorithm>, so we
need to make sure to IWYU.

[1]: https://github.com/verilog-to-routing/vtr-verilog-to-routing.git

Signed-off-by: Henner Zeller <[email protected]>

Author: hzeller

libs/libvtrutil/src/vtr_ndmatrix.h

@@ -1,5 +1,6 @@
 #ifndef VTR_ND_MATRIX_H
 #define VTR_ND_MATRIX_H
+#include <algorithm>
 #include <array>
 #include <memory>