Starting with 2013.1 Vivado Synthesis, the -no_iobuf switch is hidden. It is recommended to use the "out_of_context" option as part of the -mode switch instead of the -no_iobuf switch. The out_of_context mode turns off I/O buffer insertion for the module and marks it as OOC, to facilitate its use in the HD flow.
The -mode out_of_context switch option can be either passed to the synth_design TCL command or added to the More Options in the Synthesis Settings within the Vivado IDE.