When building with fortify enabled, GCC < 12 issues a warning on the
fortify strncat wrapper might overflow the destination buffer (the
failure is tied to -Werror).

Checked on ppc64 and x86_64.
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

When building with fortify enabled, GCC 6 issues an warning the fortify
wrapper might overflow the destination buffer.  However, GCC does not
provide a specific flag to disable the warning (the failure is tied to
-Werror).  So to avoid disable all errors, only enable the check for
GCC 7 or newer.

Checked on i686-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

If fortify is enabled, the truncated output warning is issued by
the wrapper itself:

In function ‘strncpy’,
    inlined from ‘test_strncpy’ at tester.c:505:10:
../string/bits/string_fortified.h:95:10: error: ‘__builtin_strncpy’
destination unchanged after copying no bytes from a string of length 3
[-Werror=stringop-truncation]
   95 |   return __builtin___strncpy_chk (__dest, __src, __len,
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   96 |                                   __glibc_objsize (__dest));
      |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../include/bits/string_fortified.h:1,
                 from ../string/string.h:548,
                 from ../include/string.h:60,
                 from tester.c:33,
                 from inl-tester.c:6:
In function ‘strncpy’,
    inlined from ‘test_strncpy’ at tester.c:505:10:

Checked on x86_64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

If fortify is enabled, the truncated output warning is issued by
the wrapper itself:

bug-strncat1.c: In function ‘main’:
bug-strncat1.c:14:3: error: ‘__builtin___strncat_chk’ output truncated
copying 1 byte from a string of length 2 [-Werror=stringop-truncation]
   14 |   strncat (d, "\5\6", 1);
      |   ^

Checked on x86_64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Since the _FORTIFY_SOURCE feature uses some routines of Glibc, they need to
be excluded from the fortification.

On top of that:
 - some tests explicitly verify that some level of fortification works
   appropriately, we therefore shouldn't modify the level set for them.
 - some objects need to be build with optimization disabled, which
   prevents _FORTIFY_SOURCE to be used for them.

Assembler files that implement architecture specific versions of the
fortified routines were not excluded from _FORTIFY_SOURCE as there is no
C header included that would impact their behavior.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

For strerror, this fixes commit 28aff047818eb1726394296d27b ("string:
Implement strerror in terms of strerror_l").  This commit avoids
returning NULL for strerror_l as well, although POSIX allows this
behavior for strerror_l.

Reviewed-by: Arjun Shankar <arjun@redhat.com>

These functions are about to be added to POSIX, under Austin Group
issue 986.

The fortified strlcat implementation does not raise SIGABRT if the
destination buffer does not contain a null terminator, it just
inherits the non-failing regular strlcat behavior.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

Copy strncpy tests for strndup.  Covers some basic testcases with random
strings.  Remove tests that set the destination's bytes and checked the
resulting buffer's bytes.  Remove wide character test support since
wcsndup() doesn't exist.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Copy strcpy tests for strdup.  Covers some basic testcases with random
strings.  Add a zero-length string testcase.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>