* rtl.def (NIL): Delete.
	* read-rtl.c (read_rtx): Handle (nil) like (define_constants).
	Tighten the syntax a little.

	* cfgloop.h, combine.c, cse.c, loop-iv.c, postreload.c, reload.c
	* config/alpha/alpha.c, config/alpha/alpha.h, config/arc/arc.h
	* config/arm/arm.h, config/frv/frv.h, config/i386/i386.c
	* config/i386/predicates.md, config/m32r/m32r.h
	* config/m68hc11/m68hc11.c, config/mcore/mcore.h, config/mips/mips.c
	* config/mmix/mmix.c, config/pa/pa.h, config/sh/sh.h
	* config/sparc/sparc.h, doc/tm.texi:
	Replace all occurrences of NIL with UNKNOWN.

From-SVN: r86193