versioner: assorted fixes.

Zero initialize the contents of ArchMap, keep track of the symbol name
in Declaration, remove unnecessary copies in loops.

Change-Id: I47b07755846f252b83ffc4c89547a34b2f7ab868
diff --git a/tools/versioner/src/Arch.h b/tools/versioner/src/Arch.h
index 7fdd17d..fbf7773 100644
--- a/tools/versioner/src/Arch.h
+++ b/tools/versioner/src/Arch.h
@@ -76,7 +76,7 @@
   }
 
  private:
-  std::array<T, size_t(Arch::x86_64) + 1> data_;
+  std::array<T, size_t(Arch::x86_64) + 1> data_ = {};
 };
 
 template <typename T>