Isolated emscripten in new lib

lib/emscripten/emtests/test_i64_precise_unneeded.c

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2016 The Emscripten Authors.  All rights reserved.
+ * Emscripten is available under two separate licenses, the MIT license and the
+ * University of Illinois/NCSA Open Source License.  Both these licenses can be
+ * found in the LICENSE file.
+ */
+
+#include <inttypes.h>
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+  uint64_t x = 2125299906845564, y = 1225891506842664;
+  if (argc == 12) {
+    x = x >> 1;
+    y = y >> 1;
+  }
+  x = x & 12ULL;
+  y = y | 12ULL;
+  x = x ^ y;
+  x <<= 2;
+  y >>= 3;
+  printf("*%llu, %llu*\n", x, y);
+}