PR tree-optimization/82646 - bogus -Wstringop-overflow with -D_FORTIFY_SOURCE=2 on strncpy with range to a member array

gcc/ChangeLog:

	PR tree-optimization/82646
	* builtins.c (maybe_emit_chk_warning): Use size as the bound for
	strncpy, not maxlen.

gcc/testsuite/ChangeLog:

	PR tree-optimization/82646
	* gcc.dg/builtin-stringop-chk-1.c: Adjust.
	* gcc.dg/builtin-stringop-chk-9.c: New test.
	* g++.dg/ext/strncpy-chk1.C: Adjust.

From-SVN: r255448