Template global function causes visibility warning.

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When I compile pat with 2.6.2, I got many of the warning:
{{{
ld: warning: direct access in 
pat::testing::GetBoolAssertionFailureMessage(pat::testing::AssertionResult 
const&, char const*, char const*, char const*) to global weak symbol VTT for 
pat::BasicOStrStream<char, std::__1::char_traits<char>, 
std::__1::allocator<char> > means the weak symbol cannot be overridden at 
runtime. This was likely caused by different translation units being compiled 
with different visibility settings.
}}}

I'm not sure the causes of the warning. I'm trying to change default visibility 
to remove this warning.

Original issue reported on code.google.com by luba@skymizer.com on 20 Mar 2014 at 6:52