* define global `__v_inside_init`
* unset `__v_inside_init` after `_vinit()`
* define `C.GC_MALLOC_UNCOLLECTABLE()`
* allocate uncollectable memory during `_vinit()`
* ci: run test cases with V copiler that uses GC-Boehm itself
* wrap `__v_inside_init` access into `#ifdef _VGCBOEHM`