src: fix ssize_t error from nghttp2.h

The "node_http2.h" include reordering enforced by clang-format (nodejs@32446d8#diff-33f026e43570112875cf4c8eab6743496f3aa014329611128e348ec23d6f771cR1)
broke Electron's Node.js upgrade on Windows.

```sh
In file included from ../../third_party/electron_node/src/node_http2.cc:1:
In file included from ../../third_party/electron_node/src/node_http2.h:8:
../../third_party/electron_node/deps/nghttp2/lib/includes\nghttp2/nghttp2.h(930,9): error: unknown type name 'ssize_t'
typedef ssize_t (*nghttp2_data_source_read_callback)(
        ^
```

ssize_t is a part of the POSIX standard and it's not available on
Windows, so the fix for this is to typedef it on Windows like in
https://github.com/nodejs/node/blob/bb4dff783ddb3b20c67041f7ccef796c335c2407/src/node.h#L212-L220.

Refs: electron/electron#35350 (comment)
Signed-off-by: Darshan Sen <raisinten@gmail.com>

Author: RaisinTen

src/node_http2.h

@@ -3,6 +3,20 @@
 
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
+// nghttp2.h needs ssize_t to compile on Windows.
+// Refs: https://github.com/electron/electron/pull/35350#discussion_r954890551
+// Same as
+// https://github.com/nodejs/node/blob/bb4dff783ddb3b20c67041f7ccef796c335c2407/src/node.h#L212-L220.
+#ifdef _WIN32
+#if !defined(_SSIZE_T_) && !defined(_SSIZE_T_DEFINED)
+typedef intptr_t ssize_t;
+#define _SSIZE_T_
+#define _SSIZE_T_DEFINED
+#endif
+#else                   // !_WIN32
+#include <sys/types.h>  // size_t, ssize_t
+#endif                  // _WIN32
+
 // FIXME(joyeecheung): nghttp2.h needs stdint.h to compile on Windows
 #include <cstdint>
 #include "nghttp2/nghttp2.h"