Introduce bfd_set_filename

Introduce bfd_set_filename

This introduces a new bfd_set_filename function, which is then used in
various spots in gdb.  This allows for the removal of some casts.

bfd/ChangeLog
2019-09-11  Tom Tromey  <tom@tromey.com>

	* opncls.c (bfd_set_filename): New function.
	* bfd-in2.h: Regenerate.

gdb/ChangeLog
2019-09-11  Tom Tromey  <tom@tromey.com>

	* symfile-mem.c (symbol_file_add_from_memory): Use
	bfd_set_filename.
	* solib-darwin.c (darwin_bfd_open): Use bfd_set_filename.
	* solib-aix.c (solib_aix_bfd_open): Use bfd_set_filename.