[patch] Produce .weak_def_can_be_hidden for some linkonce_odr values

[Rafael Espíndola]

>> How much do we lose
>> if you don't do this recomparison, is that tolerable? I realize that getting
>> a second run of globalopt at the end is going to be time consuming to prove
>> worthwhile, but I really think it's the right way to go.
>
> With a notaddrtaken attribute the run of GlobalOpt we have would be
> sufficient. This check is at the very end of the compilation.  I will
> benchmark a build without the GlobalStatus::analyzeGlobal and report
> as soon as the bootstrap finishes.
>

The result is far more modest:

$ nm build-patch2/bin/clang | grep ' T ' | wc

   20850   62550 1763368


>>>
>>> $ nm  build-with-master/bin/clang-3.4  | grep  ' T ' | wc
>>>
>>>    21053 63159 1790901
>>>
>>> $ nm  build-with-patch/bin/clang-3.4  | grep  ' T ' | wc
>>>
>>>    19049   57147 1547425

Cheers,
Rafael