libunwindstack: add Regs::Clone.

Add a way to copy a Regs object.

Bug: http://b/77296294
Test: libunwindstack_test
Change-Id: I28aff510aa3e1b677d5ae46dc3bfe7652817ce52
diff --git a/libunwindstack/RegsX86_64.cpp b/libunwindstack/RegsX86_64.cpp
index 7d6ad86..ebad3f4 100644
--- a/libunwindstack/RegsX86_64.cpp
+++ b/libunwindstack/RegsX86_64.cpp
@@ -168,4 +168,8 @@
   return true;
 }
 
+Regs* RegsX86_64::Clone() {
+  return new RegsX86_64(*this);
+}
+
 }  // namespace unwindstack