c-common.c, [...]: Fix comment typos.

	* c-common.c, calls.c, cfgcleanup.c, cgraph.c, cgraphunit.c,
	ddg.c, ddg.h, df.c, df.h, except.c, expr.c, flags.h,
	fold-const.c, gcc.c, gimplify.c, haifa-sched.c,
	modulo-sched.c, tree-inline.c, tree-into-ssa.c, tree-nested.c,
	tree-nrv.c, tree-ssa-ccp.c, tree-ssa-dom.c, tree-ssa-live.c,
	tree-ssa-loop.c, tree-ssa-pre.c, tree-tailcall.c, tree.h: Fix
	comment typos.  Follow spelling conventions.

From-SVN: r82439