PR23254, ld.bfd mishandles file pointers while scanning archive

PR23254, ld.bfd mishandles file pointers while scanning archive

Best practice is to not mix lseek/read with fseek/fread on the same
underlying file descriptor, as not all stdio implementations will cope.
Since the plugin uses lseek/read while bfd uses fseek/fread this patch
reopens the file for exclusive use by the plugin rather than trying to
restore the file descriptor.  That allows the plugin to read the file
after plugin_call_claim_file too.

bfd/
	PR 23254
	* plugin.c (bfd_plugin_open_input): Allow for possibility of
	nested archives.  Open file again for plugin.
	(try_claim): Don't save and restore file position.  Close file
	if not claimed.
	* sysdep.h (O_BINARY): Define.
ld/
	PR 23254
	* plugin.c (plugin_call_claim_file): Revert 2016-07-19 patch.
	(plugin_object_p): Don't dup file descriptor.