gdb/

	* elfread.c (elf_symfile_read): Limit separate debug info additions to
	files with no separate debug info.
	* objfiles.c (add_separate_debug_objfile): Add gdb_assert calls.
	* symfile.c (read_symbols): Call find_separate_debug_file_in_section
	only for files with no separate debug info.

gdb/testsuite/
	* gdb.base/gnu-debugdata.exp): Create ${binfile}.debug,
	${binfile}.mini_debuginfo-debuglink, add -k to xz, use now
	${binfile}.mini_debuginfo-debuglink and
	${binfile}.mini_debuginfo-debuglink.xz.