Configure needs to build libspidev-lib++.a

[eddelbuettel]

PR #3 only removed the compilation hurdles, you still need to add e.g. a configure script to got into the spidev library sources and build the static library. My PR assumed it built.

The vignette on package builds with a library has examples, otherwise a more recent package of mine doing just this and building a static library with cmake first is crc32c.