I got this when compiling the latest Fedora source RPM (7.5.1-32). My default CFLAGS is -O3 instead of the default -O2:

In function 'strncat',
    inlined from 'svr4_create_solib_event_breakpoints' at ../../gdb/solib-svr4.c:2076:
/usr/include/bits/string3.h:152: error: call to __builtin___strncat_chk might overflow destination buffer


this correctly fails the build. The fix was simple, as the correct use of strncat for the same data is one line below:
              if (with_prefix)
                strncat (name, "rtld_", sizeof (name));

              strncat (name, probe_info[i].name, sizeof (name) - sizeof ("rtld_"));

becomes

              if (with_prefix)
                strncat (name, "rtld_", sizeof (name) - sizeof("rtld_"));

              strncat (name, probe_info[i].name, sizeof (name) - sizeof ("rtld_"));


and this eliminates the warning/error.