use armc4random instead of getentropy

src/main/native/c/drbg.c

@@ -15,6 +15,7 @@
  *
  */
 #include <drbg.h>
+#include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
 
@@ -147,7 +148,7 @@ int generate_seed(DRBG* generator, byte output[], int n_bytes) {
     if (parent != NULL) {
         return next_rand(parent, output, n_bytes);
     } else {
-        return getentropy(output, n_bytes);
+        return arc4random_buf(output, n_bytes);
     }
 }
 
@@ -158,7 +159,7 @@ void reseed(DRBG* generator) {
 void reseed_with_params(DRBG *generator, DRBGParams *params) {
     byte seed[128]; // TODO: what should the default seed size be?
     size_t length = 128;
-    getentropy(seed, length);
+    arc4random_buf(seed, length);
     EVP_RAND_reseed(generator->context, params->prediction_resistance, seed, length, params->additional_data, params->additional_data_length);
 }