fw-c: fix compilation with system-installed clpru
fw-c: fix compilation with system-installed clpru

when clpru is system-installed it needs no help in findings its headers
and libraries, and using /usr/include and /usr/lib is very wrong.

mvduin/py-uio,mvduin/py-uio,mvduin/py-uio,mvduin/py-uio,mvduin/py-uio