[RFC] Fix BFD leak in solib-darwin.c

[Tom Tromey <tromey@adacore.com>]

commit 192b62ce0b4bb5c61188f570e127a26d2c32f716 ("Use class to manage
BFD reference counts") changed darwin_get_dyld_bfd to use:

+	dyld_bfd.release ();

rather than

-      do_cleanups (cleanup);

However, using release here leaks the BFD.  Instead I believe reset
should be used instead.

I can't readily test this, so please take a look and let me know what
you think.

gdb/ChangeLog
2019-02-22  Tom Tromey  <tromey@adacore.com>

	* solib-darwin.c (darwin_get_dyld_bfd): Use reset, not release.
---
 gdb/ChangeLog      | 4 ++++
 gdb/solib-darwin.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/gdb/solib-darwin.c b/gdb/solib-darwin.c
index d3060604bad..da410ad4660 100644
--- a/gdb/solib-darwin.c
+++ b/gdb/solib-darwin.c
@@ -455,7 +455,7 @@ darwin_get_dyld_bfd ()
       if (sub != NULL)
 	dyld_bfd = sub;
       else
-	dyld_bfd.release ();
+	dyld_bfd.reset (nullptr);
     }
   return dyld_bfd;
 }
-- 
2.20.1