You are correct, systemtap overrides the path to
'/bin:/sbin:/usr/bin:/usr/sbin' for security reasons.
My quess is that you are some sort of an embedded environment where the
compiler isn't actually there and you are trying to NFS mount it.
If that is the case, one possible solution to your problem would be to
build your module on a system where the compiler is installed in the
proper place, then transfer the module over and run it with staprun.
Note that the compile system doesn't have to be running the same kernel
as the target system, but it does have to have the target kernel
installed (and then you'd use the stap '-r RELEASE' argument).
Another possible solution to your problem is modify main.cxx to add in
your special compiler directory to our override of PATH.