Add missing file in previous commit.

This was SVN commit r24996.

source/lib/sysdep/arch/ppc64/ppc64.cpp

@@ -0,0 +1,50 @@
+/* Copyright (C) 2021 Wildfire Games.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+/*
+ * routines specific to PowerPC64
+ */
+
+#include "precompiled.h"
+
+#include "lib/sysdep/cpu.h"
+
+intptr_t cpu_AtomicAdd(volatile intptr_t* location, intptr_t increment)
+{
+	return __sync_fetch_and_add(location, increment);
+}
+
+bool cpu_CAS(volatile intptr_t* location, intptr_t expected, intptr_t newValue)
+{
+	return __sync_bool_compare_and_swap(location, expected, newValue);
+}
+
+bool cpu_CAS64(volatile i64* location, i64 expected, i64 newValue)
+{
+	return __sync_bool_compare_and_swap(location, expected, newValue);
+}
+
+const char* cpu_IdentifierString()
+{
+	// TODO
+	return "IBM POWER";
+}