[TESTSUITE]Use memcpy instead of strcpy in testsuite/gcc.dg/memcmp-1.c

[TESTSUITE]Use memcpy instead of strcpy in testsuite/gcc.dg/memcmp-1.c

strcpy will keep reading and writing memory if the string is not terminated
with null character. In this case, it may visit memory beyond the boundary.

gcc/testsuite/

2017-08-31  Renlin Li  <renlin.li@arm.com>
	    Aaron Sawdey  <acsawdey@linux.vnet.ibm.com>

	* gcc.dg/memcmp-1.c (test_strncmp): Use memcpy instead of strcpy.

Co-Authored-By: Aaron Sawdey <acsawdey@linux.vnet.ibm.com>
From-SVN: r251554