PR preprocessor/79214 - -Wno-system-header defeats strncat buffer overflow warnings

PR preprocessor/79214 -  -Wno-system-header defeats strncat buffer overflow warnings
PR middle-end/79222 - missing -Wstringop-overflow= on a stpcpy overflow
PR middle-end/79223 - missing -Wstringop-overflow on a memmove overflow

gcc/ChangeLog:

	PR preprocessor/79214
	PR middle-end/79222
	PR middle-end/79223
	* builtins.c (check_sizes): Add inlinining context and issue
	warnings even when -Wno-system-headers is set.
	(check_strncat_sizes): Same.
	(expand_builtin_strncat): Same.
	(expand_builtin_memmove): New function.
	(expand_builtin_stpncpy): Same.
	(expand_builtin): Handle memmove and stpncpy.

gcc/testsuite/ChangeLog:

	PR preprocessor/79214
	PR middle-end/79222
	PR middle-end/79223
	* gcc.dg/pr79214.c: New test.
	* gcc.dg/pr79214.h: New test header.
	* gcc.dg/pr79222.c: New test.
	* gcc.dg/pr79223.c: New test.
	* gcc.dg/pr78138.c: Adjust.
	* gfortran.dg/unconstrained_commons.f: Same.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@247618 138bc75d-0d04-0410-961f-82ee72b054a4