Disable thread support under Perl 5.8

We got some mysterious CPAN Testers failures with several 5.8 releases
when calling Err_get_error from a thread. Disable thread support under
Perl 5.8, even if 5.8.9 seems to work. (Note that version 5.10.0 has
already been blacklisted.)

http://matrix.cpantesters.org/?dist=Clownfish+0.6.2
http://www.cpantesters.org/cpan/report/4c2e4fd2-cf8c-11e7-b8bd-809199b835e7
http://www.cpantesters.org/cpan/report/a93c273a-cf8c-11e7-b8bd-809199b835e7
diff --git a/compiler/perl/lib/Clownfish/CFC/Perl/Build/Charmonic.pm b/compiler/perl/lib/Clownfish/CFC/Perl/Build/Charmonic.pm
index f109e94..5bcf4c8 100644
--- a/compiler/perl/lib/Clownfish/CFC/Perl/Build/Charmonic.pm
+++ b/compiler/perl/lib/Clownfish/CFC/Perl/Build/Charmonic.pm
@@ -108,7 +108,9 @@
     }
     # Perl 5.8.7 added support for CLONE_SKIP.
     # Thread support in 5.10.0 seems completely broken (CLOWNFISH-107).
-    if ( !$self->config('usethreads') || $^V lt v5.8.7 || $^V eq v5.10.0 ) {
+    # We also got some mysterious, thread-related CPAN Testers failures with
+    # several 5.8 releases, so disable thread support for 5.10.0 and earlier.
+    if ( !$self->config('usethreads') || $^V le v5.10.0 ) {
         push @command, '--disable-threads';
     }
     push @command, (