Print to standard error when standard output is valuable.
 [rsc] --rw-rw-r-- M 399900 glenda sys 23848 Sep 26 16:24 sys/src/cmd/cc/lex.c
	/n/sourcesdump/2005/0926/plan9/sys/src/cmd/cc/lex.c:177,183 - 
	/n/sourcesdump/2005/0927/plan9/sys/src/cmd/cc/lex.c:177,184
	  	}
	  	if((debug['a'] || debug['Z']) && !debug['n']) {
	  		outfile = 0;
	- 		Binit(&outbuf, 1, OWRITE);
	+ 		Binit(&outbuf, dup(1, -1), OWRITE);
	+ 		dup(2, 1);
	  	} else {
	  		c = mycreat(outfile, 0664);
	  		if(c < 0) {
 [sys] --rwxrwxr-x M 399900 rsc sys 358222 Sep 26 23:08 386/bin/8c
	/sys/src/cmd/cc/lex.c:compile