Fix PR 101453: ICE with optimize and large integer constant

Fix PR 101453: ICE with optimize and large integer constant

The problem is the buffer is too small to hold "-O" and
the interger.  This fixes the problem by use the correct size
instead.

Changes since v1:
* v2: Use HOST_BITS_PER_LONG and just divide by 3 instead of
3.32.

OK? Bootstrapped and tested on x86_64-linux with no regressions.

gcc/c-family/ChangeLog:

	PR c/101453
	* c-common.c (parse_optimize_options): Use the correct
	size for buffer.