Fixed the Symbol code to resolve the callable address
of the symbol itself rather than forcing clients to do
it.  This simplifies the logic for the expression
parser a great deal.

<rdar://problem/16935324>


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@209494 91177308-0d34-0410-b5e6-96231b3b80d8