detect rng seed strength at runtime based on algorithm not compile time based on platform features

include/decl.h

@@ -220,6 +220,7 @@ E NEARDATA boolean mrg_to_wielded;
 E NEARDATA boolean defer_see_monsters;
 
 E NEARDATA boolean in_steed_dismounting;
+E NEARDATA boolean has_strong_rngseed;
 
 E const int shield_static[];
 

src/decl.c

@@ -120,6 +120,7 @@ NEARDATA boolean mrg_to_wielded = FALSE;
 /* weapon picked is merged with wielded one */
 
 NEARDATA boolean in_steed_dismounting = FALSE;
+NEARDATA boolean has_strong_rngseed = FALSE;
 
 NEARDATA coord bhitpos = DUMMY;
 NEARDATA coord doors[DOORMAX] = { DUMMY };

src/hacklib.c

@@ -899,8 +899,10 @@ init_random()
 void
 reseed_random()
 {
-    /* reseed */
-    init_random();
+   /* only reseed if we are certain that the seed generation is unguessable
+    * by the players. */
+    if (has_strong_rngseed)
+        init_random();
 }
 
 time_t

sys/unix/unixmain.c

@@ -776,6 +776,7 @@ sys_random_seed()
     fptr = fopen(DEV_RANDOM, "r");
     if (fptr) {
         fread(&seed, sizeof(long), 1, fptr);
+        has_strong_rngseed = TRUE;
     }
     fclose(fptr);
 #else

sys/winnt/winnt.c

@@ -708,6 +708,7 @@ sys_random_seed(VOID_ARGS)
                                  (ULONG) sizeof ourseed, 0);
         if (status == STATUS_SUCCESS) {
             BCryptCloseAlgorithmProvider(hRa,0);
+            has_strong_rngseed = TRUE;
             Plan_B = FALSE;
         }
     }