This was motivated by the fact that constructor type homing (debug info
optimization that we want to turn on by default) drops some libc++ types,
so an attribute would allow us to override constructor homing and emit
This attribute is called __attribute__((standalone_debug)) and classes with
the attribute will get debug info in the same way as if they were built with
-fstandalone-debug. So, essentially, it overrides all of the debug info optimizations
that are used in -fstandalone-debug.