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/RegsArm.cpp b/libunwindstack/RegsArm.cpp
index 27cab43..de22bde 100644
--- a/libunwindstack/RegsArm.cpp
+++ b/libunwindstack/RegsArm.cpp
@@ -197,4 +197,8 @@
   return true;
 }
 
+Regs* RegsArm::Clone() {
+  return new RegsArm(*this);
+}
+
 }  // namespace unwindstack