PR tree-optimization/85259 - Missing -Wstringop-overflow= since r256683

PR tree-optimization/85259 - Missing -Wstringop-overflow= since r256683

gcc/ChangeLog:

	PR tree-optimization/85259
	* builtins.c (compute_objsize): Handle constant offsets.
	* gimple-ssa-warn-restrict.c (maybe_diag_offset_bounds): Return
	true iff a warning has been issued.
	* gimple.h (gimple_nonartificial_location): New function.
	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Call
	gimple_nonartificial_location and handle -Wno-system-headers.
	(handle_builtin_stxncpy): Same.

gcc/testsuite/ChangeLog:

	PR tree-optimization/85259
	* gcc.dg/Wstringop-overflow-5.c: New test.
	* gcc.dg/Wstringop-overflow-6.c: New test.

From-SVN: r261518