* Makefile.in: Regenerate.
* Makefile.def (gcc host module) and soft dependency on lto-plugin
and configure dependency on lto-plugin configure.
(lto-plugin module): Remove dependency on GCC; add dependency on
liniberty.
* doc/invoke.texi: (-flto, -fuse-linker-plugin): Update defaults
and no longer claim that gold is required for linker plugin.
* configure: Regenerate.
* gcc.c (PLUGIN_COND): New macro.
(LINK_COMMAND_SPEC): Use it.
(main): Default to plugin enabled with HAVE_LTO_PLUGIN is set.
* config.in (HAVE_LTO_PLUGIN): New.
* configure.ac (--with-lto-plugin): New parameter; autodetect
HAVE_LTO_PLUGIN.