Set up config.log earlier so that AC_MSG_ERROR and AC_MSG_WARN can

Set up config.log earlier so that AC_MSG_ERROR and AC_MSG_WARN can
be used early.
* acgeneral.m4 (_AC_INIT_DEFAULTS): Call `_AC_INIT_PREPARE_FDS'.
(_AC_INIT_PREPARE): Don't.
(_AC_INIT_PREPARE_ENVIRONMENT, _AC_INIT_PREPARE_FDS): Rename as...
(_AC_INIT_DEFAULTS_ENVIRONMENT, _AC_INIT_DEFAULTS_FDS): these,
since they are called from `_AC_INIT_DEFAULTS', not
`_AC_INIT_PREPARE'.
(_AC_INIT_DEFAULTS_FDS): Dump `$@' in config.log, not
`$ac_configure_args' which is not computed yet.