I've been using the PWM Block from SparkFun for Intel Edison recently without any issue in C programming.
My code is based on this library :
which I adapted as a C library in my program, with some minor modifications.
Also I had to make some precise measurments to retrieve the exact value of internal oscillator, which was closer to 27MHz than 25MHz in my case
There won't be much difference between using the library in C or C++ in terms of performance, both are efficient enough