Logger: Disable pthread cancel point inside Logger destructor
Logger: Disable pthread cancel point inside Logger destructor

pthread_cancel is implemented in c++ using exception handlers. In
destructor of Log object, the log function is called which will
eventually call fputs() to write to a file. Since that function is
considered a cancelation point, if pthread_cancel has been called the
exception handler will start unstacking frames and calling destructors
in the process. At some point this will cause a runtime exception in c++
which will call std::terminate() to abort the process.

The solution is thus to avoid starting the cancellation process inside the
destructor.

This behavior was spotted while calling the destructor of Transceiver
object in forthcoming patches.

See a more detailed example here:
https://skaark.wordpress.com/2010/08/26/pthread_cancel-considered-harmful/

Change-Id: I71ca90f3fbc73df58b878a03361f7b7831d838b4

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