Add no-op |RAND_load_file| function for compatibility.

Change-Id: I9493a1509a75d3f0d99ce2b699d8781ad9b1bafa
Reviewed-on: https://boringssl-review.googlesource.com/4540
Reviewed-by: Adam Langley <agl@google.com>

crypto/rand/rand.c

@@ -14,6 +14,7 @@
 
 #include <openssl/rand.h>
 
+#include <limits.h>
 #include <string.h>
 
 #include <openssl/mem.h>
@@ -149,6 +150,16 @@ int RAND_pseudo_bytes(uint8_t *buf, size_t len) {
 
 void RAND_seed(const void *buf, int num) {}
 
+int RAND_load_file(const char *path, long num) {
+  if (num < 0) {  /* read the "whole file" */
+    return 1;
+  } else if (num <= INT_MAX) {
+    return (int) num;
+  } else {
+    return INT_MAX;
+  }
+}
+
 void RAND_add(const void *buf, int num, double entropy) {}
 
 int RAND_poll(void) {

include/openssl/rand.h

@@ -41,6 +41,9 @@ OPENSSL_EXPORT int RAND_pseudo_bytes(uint8_t *buf, size_t len);
 /* RAND_seed does nothing. */
 OPENSSL_EXPORT void RAND_seed(const void *buf, int num);
 
+/* RAND_load_file returns a nonnegative number. */
+OPENSSL_EXPORT int RAND_load_file(const char *path, long num);
+
 /* RAND_add does nothing. */
 OPENSSL_EXPORT void RAND_add(const void *buf, int num, double entropy);