Instead of weak-linking against LoggingSupport framework (which

requires that this private framework be available - and it is not
available earlier than macOS 10.12 - to build lldb), dlopen the
framework binary on demand in debugserver.  We're already using
dlsym() to look up all the symbols so there is no need to use weak
linking here.

<rdar://problem/30158797> 

llvm-svn: 293135