Use C linkage for plugin initialization & termination. I'm working on
adding support for using the existing plugin infrastructure but with
dynamic libraries. Using C linkage makes it easier to dlsym the
initialize and terminate methods.
For example, with this patch,
`__ZN12lldb_private39lldb_initialize_ScriptInterpreterPythonEv` becomes
`_lldb_initialize_ScriptInterpreterPython`.
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