Isolated emscripten in new lib

lib/emscripten/emtests/FS_exports.cpp

@@ -0,0 +1,29 @@
+// Copyright 2017 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<emscripten.h>
+
+int main() {
+#ifdef USE_FILES
+  if (fopen("nonexistend", "r")) {
+    puts("that was bad");
+    return 1;
+  }
+#endif
+#ifdef DIRECT
+  EM_ASM({
+    FS.createDataFile("/", "file.txt", [1, 2, 3]);
+  });
+#else
+  EM_ASM({
+    Module["FS_createDataFile"]("/", "file.txt", [1, 2, 3]);
+  });
+#endif
+  EM_ASM({
+    // use eval, so that the compiler can't see FS usage statically
+    eval('out("Data: " + JSON.stringify(MEMFS.getFileDataAsRegularArray(FS.root.contents["file.txt"])))');
+  });
+}
+