CYGWIN: GCC prints "defined but not used" warnings on mimalloc

Bug report

Bug description:

Compiling under CYGWIN prints these warning messages:

In file included from ../cpython/Objects/mimalloc/prim/prim.c:22,
                 from ../cpython/Objects/mimalloc/static.c:37,
                 from ../cpython/Objects/obmalloc.c:23:
../cpython/Objects/mimalloc/prim/unix/prim.c:91:12: warning: ‘mi_prim_access’ defined but not used [-Wunused-function]
   91 | static int mi_prim_access(const char *fpath, int mode) {
      |            ^~~~~~~~~~~~~~
../cpython/Objects/mimalloc/prim/unix/prim.c:88:12: warning: ‘mi_prim_close’ defined but not used [-Wunused-function]
   88 | static int mi_prim_close(int fd) {
      |            ^~~~~~~~~~~~~
../cpython/Objects/mimalloc/prim/unix/prim.c:85:16: warning: ‘mi_prim_read’ defined but not used [-Wunused-function]
   85 | static ssize_t mi_prim_read(int fd, void* buf, size_t bufsize) {
      |                ^~~~~~~~~~~~
../cpython/Objects/mimalloc/prim/unix/prim.c:82:12: warning: ‘mi_prim_open’ defined but not used [-Wunused-function]
   82 | static int mi_prim_open(const char* fpath, int open_flags) {
      |            ^~~~~~~~~~~~

Looking into the code of Objects/mimalloc/prim/unix/prim.c, there is already a conditional block to avoid the generation of such warnings.
The solution for this issue is to simply add CYGWIN to that list of platforms.
So, I'm posting this issue according to the suggestion received into #146572 for tracking this change.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-146599

从 Objects/mimalloc/prim/unix/prim.c 开始，检查现有的条件代码块，该代码块用于抑制所选平台上未使用函数的警告。验证平台列表，并执行一次 Cygwin 构建，以确认这四个警告不再出现；关联的 PR gh-146599 表明相关工作已经在进行中。