[plugin] Mudflap plugin

[Rafael Espindola]

> This is great work, as I said.  I think the first steps should be to
> separate the infrastructure changes and submit them separately.

I agree!

Having mudflap as a plugin would make sure it uses a cleaner interface
to the rest of the compiler.

Some items that I think can go in first

* ) I see that you added a flag_no_builtin_alloca. If Paolo's
suggestion of calling gimple_call_set_cannot_inline doesn't work, you
can use this flag in expand_builtin_alloca instead of flag_plugin.

* ) You moved the call to initialize_plugins to compile_file. We need
to load plugins early so that things like "gcc --help -v" can display
the plugins's help. Can you add a new callback instead of moving the
call to initialize_plugins?

* ) The move of PLUGIN_FINISH_UNIT looks correct to me. Paolo, why do
you need another callback?

>
> Paolo
>

Cheers,
-- 
Rafael Avila de Espindola

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