heap use after free in xcoff_archive_info_eq

heap use after free in xcoff_archive_info_eq

Using an input file objalloc memory for anything that isn't created
when opening the bfd is not a good idea.  The problem is that this
memory can disappear if bfd_free_cached_info is called or when bfd
closes files in order to keep the number of open files reasonable.

bfd/
	* xcofflink.c (xcoff_get_archive_info): Allocate xcoff_archive_info
	on the output bfd objalloc memory.
ld/
	* testsuite/ld-scripts/sysroot-prefix.exp (single_sysroot_prefix_test):
	Log $scriptname.