compile.c: FCALL flag on AREF

* compile.c (iseq_compile_each): set FCALL flag on AREF call at
  private aref op_assign.  [ruby-core:63817] [Bug #10060]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46875 b2dd03c8-39d4-4d8f-98ff-823fe69b080e