libvlc: fix API compatibility when using libvlc from MSVC

MSVC doesn't have ssize_t but it has SSIZE_T which should be similar.

clang-cl doesn't have any ssize_t in its header and defines _MSC_VER so it
should work as well.

Co-authored-by: Martin Finkel <martin@videolabs.io>

include/vlc/libvlc_media.h

@@ -30,6 +30,12 @@
 extern "C" {
 # endif
 
+#if defined(_MSC_VER)
+#include <basetsd.h>
+typedef SSIZE_T ssize_t;
+#endif
+
+
 /** \defgroup libvlc_media LibVLC media
  * \ingroup libvlc
  * @ref libvlc_media_t is an abstract representation of a playable media.

modules/access/imem-access.c

@@ -28,6 +28,12 @@
 #include <vlc_access.h>
 #include <vlc_plugin.h>
 
+#ifdef _WIN32
+#include <basetsd.h> // ensure MSVC compatibility
+static_assert(sizeof(SSIZE_T) == sizeof(ssize_t),
+                "libvlc_media_read_cb type mismatch");
+#endif
+
 struct access_sys_t
 {
     void *opaque;