using C libraries inside verilog
Well, you might be able to do it for accelerating your simulation, but it is not possible to synthesize this and put it on an FPGA.  Verilog code is a hardware description language that describes the functionality and interconnections of your design.  It is not executed like a program, it is synthesized into the equivalent of a schematic diagram.  

You could run your FFT algorithm on a CPU that's written in verilog, but that rather defeats the purpose of using an FPGA if you need a very fast FFT.  However, there are FFT cores available, so you should not have to reinvent the wheel.  I believe the Xilinx core generator can generate one, or you can use one from a site like opencores.org.  

By the way, bit reversal, if I understand what you mean by that, should be a trivial operation on an FPGA if it's implemented correctly.