`RubyVM.keep_script_lines`

`RubyVM.keep_script_lines` enables to keep script lines
for each ISeq and AST. This feature is for debugger/REPL
support.

```ruby
RubyVM.keep_script_lines = true
RubyVM::keep_script_lines = true

eval("def foo = nil\ndef bar = nil")
pp RubyVM::InstructionSequence.of(method(:foo)).script_lines
```

1 files changed, 1 insertions, 0 deletions

diff --git a/vm_core.h b/vm_core.h
index 11af8a365d..8519da8f9e 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -433,6 +433,7 @@ struct rb_iseq_constant_body {
 
     struct {
 	rb_snum_t flip_count;
+        VALUE script_lines;
 	VALUE coverage;
         VALUE pc2branchindex;
 	VALUE *original_iseq;