make system random work in VM (#17059)

* make system random work in VM

tests/stdlib/tsysrand.nim

@@ -1,13 +1,36 @@
 discard """
   targets: "c cpp js"
+  matrix: "--experimental:vmopsDanger"
 """
 
 import std/sysrand
 
 
-doAssert urandom(0).len == 0
-doAssert urandom(10).len == 10
-doAssert urandom(20).len == 20
-doAssert urandom(120).len == 120
-doAssert urandom(113).len == 113
-doAssert urandom(1234) != urandom(1234) # unlikely to fail in practice
+template main() =
+  block:
+    var x = array[5, byte].default
+    doAssert urandom(x)
+
+  block:
+    var x = newSeq[byte](5)
+    doAssert urandom(x)
+
+  block:
+    var x = @[byte(0), 0, 0, 0, 0]
+    doAssert urandom(x)
+
+  block:
+    var x = @[byte(1), 2, 3, 4, 5]
+    doAssert urandom(x)
+
+  block:
+    doAssert urandom(0).len == 0
+    doAssert urandom(10).len == 10
+    doAssert urandom(20).len == 20
+    doAssert urandom(120).len == 120
+    doAssert urandom(113).len == 113
+    doAssert urandom(1234) != urandom(1234) # unlikely to fail in practice
+
+
+static: main()
+main()