[backtrace] Avoid segfault

https://gcc.gnu.org/ml/gcc-patches/2019-01/msg01521.html

	* elf.c (elf_add): Pass "" filename to recursive call with
	separated debug.

From-SVN: r268275

libbacktrace/ChangeLog

+2019-01-25  Nathan Sidwell  <nathan@acm.org>
+
+	* elf.c (elf_add): Pass "" filename to recursive call with
+	separated debug.
+
 2019-01-25  Tom de Vries  <tdevries@suse.de>
 
 	* elf.c (elf_add): When handling .gnu_debugaltlink, call elf_add with

libbacktrace/elf.c

@@ -3041,7 +3041,7 @@ elf_add (struct backtrace_state *state, const char *filename, int descriptor,
 	  if (debugaltlink_view_valid)
 	    backtrace_release_view (state, &debugaltlink_view, error_callback,
 				    data);
-	  ret = elf_add (state, NULL, d, base_address, error_callback, data,
+	  ret = elf_add (state, "", d, base_address, error_callback, data,
 			 fileline_fn, found_sym, found_dwarf, NULL, 0, 1, NULL,
 			 0);
 	  if (ret < 0)