perl-5.18.2-296.fc21 loads modules from system instead from build directory at some tests. E.g. t/comp/parser.t:

$ LD_PRELOAD=../libperl.so strace -fq -eopen,execve ./perl harness comp/parser.t 2>&1 |grep '"/usr/lib64/perl5/'
[pid 13545] open("/usr/lib64/perl5/re.pm", O_RDONLY) = 5
[pid 13545] open("/usr/lib64/perl5/auto/re/re.so", O_RDONLY|O_CLOEXEC) = 5

This is caused by a bug in t/TEST where _cmd() functions forgets to emit "-I" arguments if requested. The _cmd() is called with:

$VAR1 = {
          'return_dir' => undef,
          'testswitch' => '',
          'perl' => './perl',
          'file' => '',
          'utf8' => '',
          'lib' => '../lib',
          'run_dir' => undef,
          'switch' => '',
          'test' => 'comp/parser.t'
        };
$VAR2 = 'perl';

but it returns:

$VAR1 = './perl comp/parser.t ';

while it should return:

$VAR1 = './perl -I../lib comp/parser.t ';

The fix is to change line:

        $cmd = $perl . _quote_args($args) . " $test $redir";

into:
        my $lib = ($options->{lib} eq '') ? '' : " -I$options->{lib}";
        $cmd = $perl . $lib . _quote_args($args) . " $test $redir";