Ruby

Fix some warnings

• Fix unused functions when no mmap.

  shape.c:285:1: warning: unused function 'redblack_insert' [-Wunused-function]
    285 | redblack_insert(redblack_node_t * tree, ID key, rb_shape_t * value)
        | ^~~~~~~~~~~~~~~
  

• Fix unknown warning group '-Wmaybe-uninitialized' with clang.

  thread_win32.c:596:1: warning: unknown warning group '-Wmaybe-uninitialized', ignored [-Wunknown-warning-option]
    596 | COMPILER_WARNING_IGNORED(-Wmaybe-uninitialized)
        | ^
  

Co-authored-by: Nobuyoshi Nakada [email protected]