Minimal code changes to allow msvc compilation.

-add msvc ssize_t definition in compat.h
-change NUM_OS_RANDOM_BYTES to int from ssize_t in random.h

Includes squashed commit: f7dc99244c8e78dbd0196f612690efcc449c37dc

Inspired by: fbf327b13868861c2877c5754caf5a9816f2603c

src/compat.h

@@ -75,6 +75,12 @@ typedef u_int SOCKET;
 #define MAX_PATH            1024
 #endif
 
+// ssize_t is POSIX, and not present when using MSVC.
+#ifdef _MSC_VER
+#include <BaseTsd.h>
+typedef SSIZE_T ssize_t;
+#endif
+
 // As Solaris does not have the MSG_NOSIGNAL flag for send(2) syscall, it is defined as 0
 #if !defined(HAVE_MSG_NOSIGNAL) && !defined(MSG_NOSIGNAL)
 #define MSG_NOSIGNAL 0

src/random.h

@@ -121,7 +121,7 @@ public:
  * sure that the underlying OS APIs for all platforms support the number.
  * (many cap out at 256 bytes).
  */
-static const ssize_t NUM_OS_RANDOM_BYTES = 32;
+static const int NUM_OS_RANDOM_BYTES = 32;
 
 /** Get 32 bytes of system entropy. Do not use this in application code: use
  * GetStrongRandBytes instead.