[glibc] string: Fix tester build with fortify enable with gcc 6

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=784ae968113011ce832b1808d4d42369f5d2e320

commit 784ae968113011ce832b1808d4d42369f5d2e320
Author: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Date:   Tue Jul 25 12:16:41 2023 -0300

    string: Fix tester build with fortify enable with gcc 6
    
    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>

Diff:
---
 string/tester.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/string/tester.c b/string/tester.c
index da42c72141..f7d4bac5a8 100644
--- a/string/tester.c
+++ b/string/tester.c
@@ -385,8 +385,17 @@ test_strncat (void)
 
   (void) strcpy (one, "gh");
   (void) strcpy (two, "ef");
+  /* 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.  */
+#if __GNUC_PREREQ (7, 0)
   (void) strncat (one, two, 99);
   equal (one, "ghef", 5);			/* Basic test encore. */
+#else
+  equal (one, "gh", 2);
+#endif
   equal (two, "ef", 6);			/* Stomped on source? */
 
   (void) strcpy (one, "");