printf: properly handle negative field width or precision arguments.

If the field width is given by an argument (when * is used in the format specification) and the value given is negative, it should be treated like a positive field width with the - flag. If a negative argument is given for the precision, it should be treated as if the precision was not specified.

The following is an example of code that behaved incorrectly:

#include <stdio.h>
int main(void) {
        printf("%*iXX\n", -50, 123);
}

stdio.asm

@@ -4544,7 +4544,17 @@ GetSize	stz	val	assume a value of 0
 	bne	gs1
 	inc4	format	  skip the '*' char
 	lda	[argp]	  fetch the value
-	sta	val
+	bpl	fv1	  do adjustments if negative:
+	ldx	~precisionSpecified
+	bne	fv0
+	eor	#$ffff	    negative field width is like
+	inc	a	      positive with - flag
+	ldx	#1
+	stx	~leftJustify
+	bra	fv1
+fv0	lda	#0	    negative precision is ignored
+	stz	~precisionSpecified
+fv1	sta	val
 	inc	argp	  remove it from the argument list
 	inc	argp
 gs0	lda	val