S/390: PR83420: Improve hotpatch option parsing.

S/390: PR83420: Improve hotpatch option parsing.

With the attached patch we get rid of the following build failure:

/home/andreas/build/../gcc/gcc/config/s390/s390.c: In function ‘void
s390_option_override()’:
/home/andreas/build/../gcc/gcc/config/s390/s390.c:15361:16: error: ‘char*
strncpy(char*, const char*, size_t)’ specified bound 256 equals destination
size [-Werror=stringop-truncation]
        strncpy (s, opt->arg, 256);
        ~~~~~~~~^~~~~~~~~~~~~~~~~~

gcc/ChangeLog:

2017-12-18  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	PR target/83420
	* config/s390/s390.c (s390_option_override): Avoid strncpy.

From-SVN: r255777