Register the gcov "writeout" at init time. Don't list this as a d'tor. Instead,

inject some code in that will run via the "__mod_init_func" method that
registers the gcov "writeout" function to execute at exit time.

The problem is that the "__mod_term_func" method of specifying d'tors is
deprecated on Darwin. And it can lead to some ambiguities when dealing with
multiple libraries.
<rdar://problem/11110106>

llvm-svn: 157852