MDEV-4214 : main.partition_rename_longfilename fails on eCryptFS

  Adding an include file which checks whether long names are supported

mysql-test/include/support_long_file_names.inc

+--error 0,3
+--perl
+my $n = 254 - length($ENV{MYSQLTEST_VARDIR});
+my $name = $ENV{MYSQLTEST_VARDIR} . '/' . sprintf("%0${n}d", $$);
+if (!open(LONG_NAME,">$name"))
+{
+  # We cannot rely either on a particular error code, or error string
+  # to check that we indeed hit "File name too long".
+  # Instead, we will try to create a file with a short name 
+  # the same way, in the same location. If it goes all right,
+  # we will assume the problem was with the file name length
+
+  open(SHORT_NAME,">$ENV{MYSQLTEST_VARDIR}/$$") ||
+    # Even a shorter name could not be created, something else is wrong
+    die "Could not create file $ENV{MYSQLTEST_VARDIR}/$$: $!";
+  close(SHORT_NAME);
+  unlink("$ENV{MYSQLTEST_VARDIR}/$$");
+  exit(3);
+} else {
+  close(LONG_NAME);
+  unlink($name);
+  exit(0);
+}
+EOF
+
+# If perl exited with error code 0, the check has passed,
+# so the calling test will be executed. 
+# If perl exited with error code 3, it will be caught by
+# --error above, and processed by the check below.
+# If perl exited with some other error code, something went wrong,
+# so the test will fail.
+
+if ($errno)
+{
+  --skip Long file names are not supported
+}
+

mysql-test/t/partition_rename_longfilename.test

 -- source include/not_windows.inc
+-- source include/support_long_file_names.inc
 -- source include/have_partition.inc
 -- source include/not_embedded.inc
 --disable_warnings