SyntheticChildrenFrontEnd::* should also be built when python is disabled

Summary:
This moves
- SyntheticChildrenFrontEnd::CreateValueObjectFromExpression
- SyntheticChildrenFrontEnd::CreateValueObjectFromAddress
- SyntheticChildrenFrontEnd::CreateValueObjectFromData
outside the `#ifndef LLDB_DISABLE_PYTHON` since it doesn't seem to depend on python being available and indeed breaks the build when python is disabled.

Reviewers: granata.enrico

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D6646