[NaCl SDK] nacl_io: Enable isatty running under sel_ldr.

native_client_sdk/src/libraries/nacl_io/passthroughfs/passthrough_fs.cc

Index: native_client_sdk/src/libraries/nacl_io/passthroughfs/passthrough_fs.cc
diff --git a/native_client_sdk/src/libraries/nacl_io/passthroughfs/passthrough_fs.cc b/native_client_sdk/src/libraries/nacl_io/passthroughfs/passthrough_fs.cc
index 4b654f19c220d2e410f470d06f834d5b1d8cd717..ebbec7d042a1b1a19fd3a915a04c4eaef13ea4b6 100644
--- a/native_client_sdk/src/libraries/nacl_io/passthroughfs/passthrough_fs.cc
+++ b/native_client_sdk/src/libraries/nacl_io/passthroughfs/passthrough_fs.cc
@@ -90,6 +90,19 @@ class PassthroughFsNode : public Node {
     return 0;
   }
 
+  virtual Error Isatty() {
+#ifdef __GLIBC__
+    // isatty is not yet hooked up to the IRT interface under glibc.
+    return ENOTTY;
+#else
+    int result = 0;
+    int err = _real_isatty(real_fd_, &result);
+    if (err)
+      return err;
+    return 0;
+#endif
+  }
+
   Error MMap(void* addr,
              size_t length,
              int prot,