re PR c/89495 (gcc/c-family/c-format.c:1272:20: runtime error: signed integer overflow: 214748365 * 10 cannot be represented in type 'int')

	PR c/89495
	* c-format.c (maybe_read_dollar_number): Compute nargnum in
	HOST_WIDE_INT type to avoid overflows and change overflow_flag
	checking.

From-SVN: r269198