* ltmain.in: Convert *each* occurrence of `compile_command',

* ltmain.in: Convert *each* occurrence of `compile_command',
`finalize_command', `relink_command', and `link_command',
that can conceivably be longer than 4000 bytes, to newline-
separated arguments before feeding to sed, to cater for sed
implementations with limited line lengths.  Convert back
afterwards.
* tests/link.test: Accommodate for trailing white space
resulting from above change.
This addresses an issue reported by Albert Chin on 2001-05-27:
http://lists.gnu.org/archive/html/libtool/2001-05/msg00159.html