Store the source range of a CXXOperatorCallExpr in the Expr object instead of

Store the source range of a CXXOperatorCallExpr in the Expr object instead of
calculating it recursively.

boost::assign::tuple_list_of uses the trick of chaining call operator expressions in order to declare a "list of tuples", e.g:
    std::vector<tuple> v = boost::assign::tuple_list_of(1, "foo")(2, "bar")(3, "qqq");

Due to CXXOperatorCallExpr calculating its source range recursively we would get
significant slowdowns with a large number of chained call operator expressions and the
potential for stack overflow.

rdar://11350116

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@155848 91177308-0d34-0410-b5e6-96231b3b80d8