Destructors for mutex and condition_variable wrongly noexcept

[niklas88]

Compiling with g++ 6.3.1 I get the following warnings

error.txt

it seems to me that these are genuine and that ~mutex() and ~condition_variable() may indeed throw while being assumed noexcept by C++11 rules. I'm not an expert on this but adding the relevant noexcept(false) declarations as well as some follow ups fixes the warning. These changes are available as a pull request of course.