avutil: fix build failure on osx 10.4

libavutil/random_seed.c calls arc4random_buf which is
not available on OSX 10.4 Tiger, but the configuration
script tests for arc4random which is available.

Fix the configuration test to match the actual API used.

Co-authored-by: James Almer <jamrial@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -2301,7 +2301,7 @@ SYSTEM_FEATURES="
 SYSTEM_FUNCS="
     access
     aligned_malloc
-    arc4random
+    arc4random_buf
     clock_gettime
     closesocket
     CommandLineToArgvW
@@ -6381,7 +6381,7 @@ check_func  ${malloc_prefix}memalign            && enable memalign
 check_func  ${malloc_prefix}posix_memalign      && enable posix_memalign
 
 check_func  access
-check_func_headers stdlib.h arc4random
+check_func_headers stdlib.h arc4random_buf
 check_lib   clock_gettime time.h clock_gettime || check_lib clock_gettime time.h clock_gettime -lrt
 check_func  fcntl
 check_func  fork

libavutil/random_seed.c

@@ -142,7 +142,7 @@ int av_random_bytes(uint8_t* buf, size_t len)
     }
 #endif
 
-#if HAVE_ARC4RANDOM
+#if HAVE_ARC4RANDOM_BUF
     arc4random_buf(buf, len);
     return 0;
 #endif