Adding myself as the code owner for the attribute subsystem.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199151 91177308-0d34-0410-b5e6-96231b3b80d8

CODE_OWNERS.TXT

@@ -8,6 +8,10 @@ beautification by scripts.  The fields are: name (N), email (E), web-address
 (W), PGP key ID and fingerprint (P), description (D), and snail-mail address
 (S).
 
+N: Aaron Ballman
+E: aaron@aaronballman.com
+D: Clang attributes
+
 N: Chandler Carruth
 E: chandlerc@gmail.com
 E: chandlerc@google.com