Windows: added alternative to bcrypt lib

src/arch_win32.h

@@ -57,6 +57,7 @@ typedef enum { false = 0, true = 1 } bool;
 #endif
 #include <wincrypt.h>
 #pragma comment(lib, "advapi32.lib")
+#elif defined(_CRT_RAND_S)
 #else
 #include <bcrypt.h>
 #if defined(_MSC_VER)

src/util.c

@@ -30,6 +30,17 @@ bool mg_random(void *buf, size_t len) {
   if (initialised == true) {
     success = CryptGenRandom(hProv, len, p);
   }
+#elif defined(_CRT_RAND_S)
+  size_t i;
+  for (i = 0; i < len; i++) {
+    unsigned int rand_v;
+    if (rand_s(&rand_v) == 0) {
+      p[i] = (unsigned char)(rand_v & 255);
+    } else {
+      break;
+    }
+  }
+  success = (i == len);
 #else
   // BCrypt is a "new generation" strong crypto API, so try it first
   static BCRYPT_ALG_HANDLE hProv;