There's currently no option for running C directly on HANA. That's the straight-forward answer.
A handful of customers write some code in L, but this needs to be a discussion between the customer and SAP. It's not generally supported.
The question in my mind is why you need to run C on HANA. The ideal coding paradigm on HANA is to run data-intensive, declarative code that HANA can massively parallelize and optimize. Generally this kind of code is logic that supports business applications that doesn't require a lower-level language like C.
Besides, simply moving C onto HANA wouldn't get you a whole lot of benefit without parallelizing your code, leveraging HANA's internal data structures, etc.
I don't see any urgent need for SAP to support this. Is it a pain to refactor code into SQLScript, R, BFL/PAL calls, etc? Sure - but that's unfortunately the name of the game. That's why they call HANA a "disruptive" technology (among other reasons).