Fix a potential illegal memory access when testing for a special LTO symbol name.

bfd	* linker.c (_bfd_generic_link_add_one_symbol): Test for a NULL
	name before checking to see if the symbol is __gnu_lto_slim.
	* archive.c (_bfd_compute_and_write_armap): Likewise.
binutils
	* nm.c (filter_symbols): Test for a NULL name before checking to
	see if the symbol is __gnu_lto_slim.
	* objcopy.c (filter_symbols): Likewise.