Fix embedding with MSVC (#44976)

(cherry picked from commit c589e0d)

Author: barche

src/support/dtypes.h

@@ -29,6 +29,16 @@
 #include <stdlib.h>
 #include <sys/stat.h>
 
+#if defined(_COMPILER_MICROSOFT_) && !defined(_SSIZE_T_) && !defined(_SSIZE_T_DEFINED)
+
+/* See https://github.com/JuliaLang/julia/pull/44587 */
+typedef intptr_t ssize_t;
+#define SSIZE_MAX INTPTR_MAX
+#define _SSIZE_T_
+#define _SSIZE_T_DEFINED
+
+#endif /* defined(_COMPILER_MICROSOFT_) && !defined(_SSIZE_T_) && !defined(_SSIZE_T_DEFINED) */
+
 #if !defined(_COMPILER_GCC_)
 
 #define strtoull                                            _strtoui64