bpo-32436: Don't use native popcount() (also fixes bpo-32641) (#5292)

diff --git a/Python/context.c b/Python/context.c
index 2f1d0f5..5439531 100644
--- a/Python/context.c
+++ b/Python/context.c
@@ -1171,7 +1171,7 @@
 int
 PyContext_ClearFreeList(void)
 {
-    int size = ctx_freelist_len;
+    Py_ssize_t size = ctx_freelist_len;
     while (ctx_freelist_len) {
         PyContext *ctx = ctx_freelist;
         ctx_freelist = (PyContext *)ctx->ctx_weakreflist;