Create `defer` syntax and `OP_PUSHDEFER` opcode

Adds syntax `defer { BLOCK }` to create a deferred block; code that is
deferred until the scope exits. This syntax is guarded by

  use feature 'defer';

Adds a new opcode, `OP_PUSHDEFER`, which is a LOGOP whose `op_other` field
gives the start of an optree to be deferred until scope exit. That op
pointer will be stored on the save stack and invoked as part of scope
unwind.

Included is support for `B::Deparse` to deparse the optree back into
syntax.

1 files changed, 1 insertions, 0 deletions

diff --git a/scope.c b/scope.c
index 8119c4ac63..55e15c8538 100644
--- a/scope.c
+++ b/scope.c
@@ -1531,6 +1531,7 @@ Perl_cx_dump(pTHX_ PERL_CONTEXT *cx)
     switch (CxTYPE(cx)) {
     case CXt_NULL:
     case CXt_BLOCK:
+    case CXt_DEFER:
         break;
     case CXt_FORMAT:
         PerlIO_printf(Perl_debug_log, "BLK_FORMAT.CV = 0x%" UVxf "\n",