logrotate: fix build with gcc 6

logrotate: fix build with gcc 6

With gcc version 6, we get the following error when building logrotate:

  logrotate.c: In function 'postrotateSingleLog':
  logrotate.c:1784:5: error: this 'if' clause does not guard... [-Werror=misleading-indentation]
       if (!state->doRotate)
       ^~
  logrotate.c:1787:2: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'if'
    if (!hasErrors && log->flags & LOG_FLAG_TMPFILENAME) {
    ^~

This is fixed by grabbing an upstream commit,
6a36c105587b07ad14fc937f3ee6e2eb402621a2. Once this is fixed, we get:

  config.c: In function 'strndup':
  config.c:87:10: error: nonnull argument 's' compared to NULL [-Werror=nonnull-compare]
          if(!s)
            ^
  cc1: all warnings being treated as errors
  make[2]: *** [config.o] Error 1
  make[2]: *** Waiting for unfinished jobs....
  cc1: all warnings being treated as errors
  make[2]: *** [logrotate.o] Error 1

This is due to logrotate providing its own implementation of
strndup(). We could fix it, but it much better to simply use the one
provided by the C library, by fixing the detection method for strndup
availability. This is done in patch
0002-Use-autoconf-checks-for-strndup-and-asprintf.patch.

Fixes:

  http://autobuild.buildroot.net/results/6dc2eb22104076920d77425b1e608ef9b9e01c94/

Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Rahul Bedarkar <rahul.bedarkar@imgtec.com>
[Thomas: replace fix for the nonnull issue with a different one.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>