[Bug libobjc/48626] --enable-objc-gc should be automatic

["iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=48626

--- Comment #5 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Eric Gallager from comment #4)
> (In reply to Eric Gallager from comment #3)
> > I'll probably keep --enable-objc-gc in my configure flags anyways even if it
> > becomes automatic, but becoming automatic could help increase test coverage
> > of it. I guess I'll confirm this.
> 
> Note that Iain Sandoe generally prefers configure detecting things
> automatically instead of requiring additional flags; I'm not quite sure how
> to go about making this one automatic now that boehm-gc is no longer
> in-tree, though.

this seems to be another set of crossed wires.

Darwin only ever used boehm-gc for Java, not for NeXT ObjC

the configure option is related to GC for the GNU runtime.  In that case, the
configuration should work the same as it does for Linux.

===

The NeXT GC support (if it was implemented, which it isn't) on Darwin uses
system-provided libraries (libauto.dylib).  Objective-C GC was retired sometime
around darwin16, so the motivation is low to put effort into implementing it
ahead of more critical missing pieces.