dtc(1): Update to 0892ec7; HACKING and implicit header fixes

Fixes courtesy of arichardson and jmg:
- HACKING was pointing to the wrong place
- Added headers were being relied on implicitly, but libstdc++ did not
  comply with the unspoken wishes of dtc.

MFC after:	1 week

usr.bin/dtc/HACKING

@@ -8,9 +8,9 @@ This file contains some notes for people wishing to hack on dtc.
 Upstreaming
 -----------
 
-This code is developed in the FreeBSD svn repository:
+This code is developed in the git repository:
 
-https://svn.freebsd.org/base/head/usr.bin/dtc
+https://github.com/davidchisnall/dtc
 
 If you got the source from anywhere else and wish to make changes, please
 ensure that you are working against the latest version, or you may end up

usr.bin/dtc/string.cc

@@ -36,6 +36,7 @@
 #include <functional>
 #include <cstdio>
 #include <cstdlib>
+#include <cstring>
 #include <ctype.h>
 #include <libgen.h>
 

usr.bin/dtc/util.hh

@@ -35,6 +35,9 @@
 #ifndef _UTIL_HH_
 #define _UTIL_HH_
 
+#include <memory>
+#include <stdint.h>
+#include <string>
 #include <vector>
 
 // If we aren't using C++11, then just ignore static asserts.