OCaml 5.0 support

[dannywillems]

Currently, when adding 5.0.0 in the CI, we get:

 warning: vendor/boxroot/boxroot.c: In function ‘pool_remove’:
warning: vendor/boxroot/boxroot.c:360:31: warning: unused variable ‘cl’ [-Wunused-variable]
warning:   360 |   FOREACH_GLOBAL_RING(global, cl, {
warning:       |                               ^~
warning: vendor/boxroot/boxroot.c:164:13: note: in definition of macro ‘FOREACH_GLOBAL_RING’
warning:   164 |       class cl = global_ring_classes[b__i - b__st];                     \
warning:       |             ^~
warning: vendor/boxroot/boxroot.c: In function ‘free_all_chunks’:
warning: vendor/boxroot/boxroot.c:375:31: warning: unused variable ‘cl’ [-Wunused-variable]
warning:   375 |   FOREACH_GLOBAL_RING(global, cl, { *global = NULL; });
warning:       |                               ^~
warning: vendor/boxroot/boxroot.c:164:13: note: in definition of macro ‘FOREACH_GLOBAL_RING’
warning:   164 |       class cl = global_ring_classes[b__i - b__st];                     \
warning:       |             ^~
warning: vendor/boxroot/boxroot.c: In function ‘promotion_occupancy’:
warning: vendor/boxroot/boxroot.c:521:17: warning: comparison of integer expressions of different signedness: ‘int’ and ‘long unsigned int’ [-Wsign-compare]
warning:   521 |   if (threshold <= LOW_COUNT_THRESHOLD) return LOW;
warning:       |                 ^~
warning: vendor/boxroot/boxroot.c:522:17: warning: comparison of integer expressions of different signedness: ‘int’ and ‘long unsigned int’ [-Wsign-compare]
warning:   522 |   if (threshold <= HIGH_COUNT_THRESHOLD) return HIGH;
warning:       |                 ^~
warning: vendor/boxroot/boxroot.c: In function ‘pool_reclassify’:
warning: vendor/boxroot/boxroot.c:544:3: warning: enumeration value ‘NO_CHANGE’ not handled in switch [-Wswitch]
warning:   544 |   switch (occ) {
warning:       |   ^~~~~~
warning: vendor/boxroot/boxroot.c: In function ‘scan_pool’:
warning: vendor/boxroot/boxroot.c:821:14: warning: passing argument 1 of ‘action’ makes pointer from integer without a cast [-Wint-conversion]
warning:   821 |       action(v, (value *)current);
warning:       |              ^
warning:       |              |
warning:       |              value {aka long int}
warning: vendor/boxroot/boxroot.c:821:14: note: expected ‘void *’ but argument is of type ‘value’ {aka ‘long int’}
warning: vendor/boxroot/boxroot.c:821:17: warning: passing argument 2 of ‘action’ makes integer from pointer without a cast [-Wint-conversion]
warning:   821 |       action(v, (value *)current);
warning:       |                 ^~~~~~~~~~~~~~~~
warning:       |                 |
warning:       |                 value * {aka long int *}
warning: vendor/boxroot/boxroot.c:821:17: note: expected ‘value’ {aka ‘long int’} but argument is of type ‘value *’ {aka ‘long int *’}
warning: vendor/boxroot/boxroot.c:821:7: error: too few arguments to function ‘action’
warning:   821 |       action(v, (value *)current);
warning:       |       ^~~~~~
warning: vendor/boxroot/boxroot.c: In function ‘boxroot_setup’:
warning: vendor/boxroot/boxroot.c:1043:31: warning: unused variable ‘cl’ [-Wunused-variable]
warning:  1043 |   FOREACH_GLOBAL_RING(global, cl, { *global = NULL; });
warning:       |                               ^~
warning: vendor/boxroot/boxroot.c:164:13: note: in definition of macro ‘FOREACH_GLOBAL_RING’
warning:   164 |       class cl = global_ring_classes[b__i - b__st];                     \
warning:       |             ^~
warning: vendor/boxroot/boxroot.c:1045:24: warning: assignment to ‘void (*)(void (*)(void *, value,  volatile value *))’ {aka ‘void (*)(void (*)(void *, long int,  volatile long int *))’} from incompatible pointer type ‘scan_roots_hook’ {aka ‘void (*)(void (*)(void *, long int,  volatile long int *), scanning_action_flags,  void *, caml_domain_state *)’} [-Wincompatible-pointer-types]
warning:  1045 |   prev_scan_roots_hook = caml_scan_roots_hook;
warning:       |                        ^
warning: vendor/boxroot/boxroot.c:1049:24: warning: assignment to ‘scan_roots_hook’ {aka ‘void (*)(void (*)(void *, long int,  volatile long int *), scanning_action_flags,  void *, caml_domain_state *)’} from incompatible pointer type ‘void (*)(void (*)(void *, value,  volatile value *))’ {aka ‘void (*)(void (*)(void *, long int,  volatile long int *))’} [-Wincompatible-pointer-types]
warning:  1049 |   caml_scan_roots_hook = scanning_callback;
warning:       |                        ^
warning: vendor/boxroot/boxroot.c: In function ‘boxroot_teardown’:
warning: vendor/boxroot/boxroot.c:1061:24: warning: assignment to ‘scan_roots_hook’ {aka ‘void (*)(void (*)(void *, long int,  volatile long int *), scanning_action_flags,  void *, caml_domain_state *)’} from incompatible pointer type ‘void (*)(void (*)(void *, value,  volatile value *))’ {aka ‘void (*)(void (*)(void *, long int,  volatile long int *))’} [-Wincompatible-pointer-types]
warning:  1061 |   caml_scan_roots_hook = prev_scan_roots_hook;
warning:       |                        ^

error: failed to run custom build command for `ocaml-boxroot-sys v0.2.0`

Might be related to ocaml-boxroot version.
It is not a priority right now as Mina uses OCaml 4.14.

[dannywillems]

Keeping an eye on zshipko/ocaml-rs#127

[dannywillems]

And also related to zshipko/ocaml-rs#125