added system.unsafeAddr

tests/ccgbugs/tunsafeaddr.nim

@@ -0,0 +1,19 @@
+discard """
+  output: '''12'''
+"""
+
+{.emit: """
+long sum(long* a, long len) {
+  long i, result = 0;
+  for (i = 0; i < len; ++i) result += a[i];
+  return result;
+}
+""".}
+
+proc sum(a: ptr int; len: int): int {.importc, nodecl.}
+
+proc main =
+  let foo = [8, 3, 1]
+  echo sum(unsafeAddr foo[0], foo.len)
+
+main()