r227487 breaks C++ programs that use __isthreaded

[David Schultz]

On Thu, Dec 01, 2011, George Liaskos wrote:
> Hello
> 
> One example is Google's tcmalloc [1], is this behaviour intended?
> 
> [1] http://code.google.com/p/google-perftools/source/browse/trunk/src/maybe_threads.cc

This code uses an unportable workaround for a bug that I believe
was fixed in r227999.  Using internal names starting with a double
underscore isn't supported.

Separately, I'm still hoping that the namespace polution
introduced in r227487 gets fixed...