* configure.in: Switch more things to use maybe dependencies.
Rearrange a little. Use GCC_TOPLEV_SUBDIRS.
* configure: Regenerate.
* Makefile.tpl: Switch more things to use maybe dependencies.
* Makefile.in: Regenerate.
<config>
* config/acx.m4: Introduce _GCC_TOPLEV_NONCANONICAL_BUILD,
_GCC_TOPLEV_NONCANOICAL_HOST, _GCC_TOPLEV_NONCANONICAL_TARGET,
GCC_TOPLEV_SUBDIRS.
(NCN_STRICT_CHECK_TOOL): If program is not found and
value-if-not-found is empty, use ${ncn_tool_prefix}$2 or $2,
depending on whether build != host or not.
(NCN_STRICT_CHECK_TARGET_TOOL): Ditto, with the target prefix.
