Vendor valgrind headers

This is encouraged according to https://valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.clientreq

third_party/valgrind/dhat.h

@@ -0,0 +1,86 @@
+
+/*
+   ----------------------------------------------------------------
+
+   Notice that the following BSD-style license applies to this one
+   file (dhat.h) only.  The rest of Valgrind is licensed under the
+   terms of the GNU General Public License, version 2, unless
+   otherwise indicated.  See the COPYING file in the source
+   distribution for details.
+
+   ----------------------------------------------------------------
+
+   This file is part of DHAT, a Valgrind tool for profiling the
+   heap usage of programs.
+
+   Copyright (C) 2020 Nicholas Nethercote.  All rights reserved.
+
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions
+   are met:
+
+   1. Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+   2. The origin of this software must not be misrepresented; you must
+      not claim that you wrote the original software.  If you use this
+      software in a product, an acknowledgment in the product
+      documentation would be appreciated but is not required.
+
+   3. Altered source versions must be plainly marked as such, and must
+      not be misrepresented as being the original software.
+
+   4. The name of the author may not be used to endorse or promote
+      products derived from this software without specific prior written
+      permission.
+
+   THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
+   OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+   WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+   ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+   DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+   DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
+   GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+   WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+   ----------------------------------------------------------------
+
+   Notice that the above BSD-style license applies to this one file
+   (memcheck.h) only.  The entire rest of Valgrind is licensed under
+   the terms of the GNU General Public License, version 2.  See the
+   COPYING file in the source distribution for details.
+
+   ----------------------------------------------------------------
+*/
+
+#if !defined(VALGRIND_DHAT_H)
+#define VALGRIND_DHAT_H
+
+#include "valgrind.h"
+
+typedef
+   enum {
+      VG_USERREQ__DHAT_AD_HOC_EVENT = VG_USERREQ_TOOL_BASE('D', 'H'),
+      VG_USERREQ__DHAT_HISTOGRAM_MEMORY,
+
+      // This is just for DHAT's internal use. Don't use it.
+      _VG_USERREQ__DHAT_COPY = VG_USERREQ_TOOL_BASE('D','H') + 256
+   } Vg_DHATClientRequest;
+
+// Record an ad hoc event. The meaning of the weight argument will depend on
+// what the event represents, which is up to the user. If no meaningful weight
+// argument exists, just use 1.
+#define DHAT_AD_HOC_EVENT(_qzz_weight) \
+    VALGRIND_DO_CLIENT_REQUEST_STMT(VG_USERREQ__DHAT_AD_HOC_EVENT, \
+                                    (_qzz_weight), 0, 0, 0, 0)
+
+// for access count histograms of memory larger than 1k
+#define DHAT_HISTOGRAM_MEMORY(_qzz_address) \
+    VALGRIND_DO_CLIENT_REQUEST_STMT(VG_USERREQ__DHAT_HISTOGRAM_MEMORY, \
+                                    (_qzz_address), 0, 0, 0, 0)
+
+#endif
+