Fix use of GNU old-style field designator extension

[MisterDA]

bindings.c:55:3: warning: use of GNU old-style field designator extension [-Wgnu-designator]
  identifier : "tree handling",
  ^~~~~~~~~~~~
  .identifier =

Security

• Change has no security implications (otherwise, ping the security team)

[mjambon]

Where do the new fields under ifdefs come from? I expect this code to be copied from the original tree-sitter bindings for Reason. The project I found is oni2 and doesn't have the ifdefs: https://github.com/onivim/oni2/blob/161a92c2226728b37cd9a6f554b7397f4beb3d5e/src/reason-tree-sitter/bindings.c#L45-L61

Can you please include an authoritative source URL at the beginning of this file?

[mjambon]

There's also https://github.com/onivim/reason-tree-sitter/blob/master/src/bindings.c but the project was archived (and it also doesn't have the ifdefs).

[MisterDA]

They were introduced in OCaml 5.0, see caml/custom.h. Using the #ifdef allows the code to remain compatible with OCaml 4 (one could also use the OCAML_VERSION macro, but I find this pattern rather elegant). Some compilers in some settings complain if some fields are left uninitialized.