Fix FreeBSD build by including utilstrencodings.h

`random.cpp` needs to explicitly include `utilstrencodings.h` to get
`ARRAYLEN`. This fixes the FreeBSD build.

This was broken in 84f4194.

Author: laanwj

src/random.cpp

@@ -34,6 +34,7 @@
 #include <sys/random.h>
 #endif
 #ifdef HAVE_SYSCTL_ARND
+#include <utilstrencodings.h> // for ARRAYLEN
 #include <sys/sysctl.h>
 #endif