No caller sets this to `true`. Initially added for and set by
`SymbolFileDWARFDebugMap` (see
`616f490777a4f35269a23abee851680134050065`). This was then removed
shortly after in:
```
commit 762f7135e290696595b6c7233245581f59eeb07c
Author: Greg Clayton <gclayton@apple.com>
Date: Sun Sep 18 18:59:15 2011 +0000
Don't put modules for .o files into the global shared module list. We
used to do this because we needed to find the shared pointer for a .o
file when the .o file's module was needed in a SymbolContext since the
module in a symbol context was a shared pointer. Now that we are using
intrusive pointers we don't have this limitation anymore since any
instrusive shared pointer can be made from a pointer to an object
all on its own.
```
At this point it's more of a foot-gun, because forcing it to true has
potentially significant performance implications (e.g.,
a5eaa05dce)
f74c2668cc