Simplify debug info back to just "limited" or "full" by rolling the ctor
type homing fully into the "limited" debug info.
Also fix a bug I found along the way that was causing ctor type homing
to kick in even when something could be vtable homed (where vtable
homing is stronger/more effective than ctor homing) - fixing at the same
time as it keeps the tests (that were testing only "limited non ctor"
homing and now test ctor homing) passing.
This adds a cc1 flag to enable constructor homing but doesn't turn on debug
info if it wasn't enabled already (which is what using
-debug-info-kind=constructor does). This will be used for testing, and won't
be needed anymore once ctor homing is used as default / merged into =limited.
Bug to enable ctor homing: https://bugs.llvm.org/show_bug.cgi?id=46537
Differential Revision: https://reviews.llvm.org/D85799
David Blaikie