High Level Synthesis of a Microprocessor
This article by Ken Chapman goes through the design process that was used to create the PicoBlaze processor used in Xilinx FPGAs.

https://www.dc.uba.ar/materias/disfpga/2010/c2/descargas/TechXclusive%20Creating%20Embedded%20Microcontrollers.pdf

The article doesn't specifically talk about C.  But the point is to try and implement the logic in a similar way to what is described.