Adjust for autoconf merger.

Adjust for autoconf merger.
	* config.h.in: Add extra line to top, in case autoconf gets fixed
	and decides not to add Makefile-style comments to the top of the
	files it generates which we are forced to lop off.
	Indicate that the boolean macros here get their definitions via
	the DEFS Makefile variable.
	Adjust the operating system and machine #includes to use
	autoload's @cookies@.
	(RETSIGTYPE): Give this a default value.
	(SIGTYPE): Set this from RETSIGTYPE.
	(LD_SWITCH_X_SITE, C_SWITCH_X_SITE): Get values via @cookies@.
	* Makefile.in (DEFS): Renamed from CONFIG_CFLAGS.
	(xmakefile): Pass CFLAGS to ${CPP}.