Don't crash when a SBType is handed out through the API and later used after...

Don't crash when a SBType is handed out through the API and later used after the module that owns the type is deleted.

The fix adds a std::weak_ptr<Module> into the TypeImpl and fills in the weak pointer when possible. It also checks to make sure the module is still alive prior to using it which should make our API safer to use.

<rdar://problem/15455145> 

llvm-svn: 212853