Change `nomp_init()` API

[thilinarmtb]

Currently, nomp_init() has the following signature:

int nomp_init(int argc, const char **argv);

This should be change similar to MPI_Init() as follows:

int nomp_init(int *argc, const char ***argv);

This way we can filter out and process --nomp-<arg> arguments and
their values and return the modified argc and argv variables without
--nomp-<arg> back to the user.