* configure.in: Introduce BASE_CC_FOR_TARGET.
* Makefile.tpl: Reorganize and comment. Introduce HOST_CONFIGARGS.
Realize configure-build-* targets. Realize configure-target-* targets.
* configure.in: Introduce BASE_CC_FOR_TARGET.
* Makefile.tpl: Reorganize and comment. Introduce HOST_CONFIGARGS.
Realize configure-build-* targets. Realize configure-target-* targets.