Put arc4random check under DISABLE_EXTRA_LIBS=OFF in CMakeLists.txt.

CMakeLists.txt

@@ -171,7 +171,9 @@ check_symbol_exists(vasprintf       "stdio.h" HAVE_VASPRINTF)
 check_symbol_exists(vsnprintf       "stdio.h" HAVE_VSNPRINTF)
 check_symbol_exists(vprintf         "stdio.h" HAVE_VPRINTF)
 
-check_symbol_exists(arc4random      "stdlib.h" HAVE_ARC4RANDOM)
+if (DISABLE_EXTRA_LIBS STREQUAL "OFF")
+    check_symbol_exists(arc4random      "stdlib.h" HAVE_ARC4RANDOM)
+endif()
 if (NOT HAVE_ARC4RANDOM AND DISABLE_EXTRA_LIBS STREQUAL "OFF")
     check_include_file(bsd/stdlib.h HAVE_BSD_STDLIB_H)
     if (HAVE_BSD_STDLIB_H)