preserve code blocks in interpolated qr//s

This now works:

    { my $x = 1; $r = qr/(??{$x})/ }
    my $x = 2;
    print "ok\n" if "1" =~ /^$r$/;

When a qr// is interpolated into another pattern, the pattern is still
recompiled using the stringified qr, but now the pre-compiled code blocks
from the qr are reused rather than being re-compiled, so it behaves like a
closure.

Note that this makes some tests in regexp_qr_embed_thr.t fail, due to a
pre-existing threads bug, which can be summarised as:

    use threads;
    my $s = threads->new(sub { return sub { $::x = 1} })->join;
    $s->();
    print "\$::x=[$::x]\n";

which prints undef, not 1, since the *::x is cloned into the child thread,
then cloned back into the parent as part of the CV (linked from the pad)
being returned in the join. The cloning/join code isn't clever enough
to realise that the back-cloned *::x is the same as the original *::x, so
the main thread ends up with two copies.

This manifests itself in the re tests as

    my $re = threads->new( sub { qr/(?{$::x = 1 })/ })->join();

where, since the returned qr// is now a closure, it suffers from the same
glob duplication in the parent.

So I've disabled 4 re_tests tests under threads for now.

1 files changed, 1 insertions, 0 deletions

diff --git a/regcomp.h b/regcomp.h
index d7261db903..f130734b70 100644
--- a/regcomp.h
+++ b/regcomp.h
@@ -542,6 +542,7 @@ END_EXTERN_C
  *   n - Root of op tree for (?{EVAL}) item
  *   o - Start op for (?{EVAL}) item
  *   p - Pad for (?{EVAL}) item
+ *   r - pointer to an embedded code-containing qr, e.g. /ab$qr/
  *   s - swash for Unicode-style character class, and the multicharacter
  *       strings resulting from casefolding the single-character entries
  *       in the character class