If a client generated with duneproject/built with dunecontrol has a
dependency to opm-autodiff, the macros defined in this file is expected
to exist and will be called to search for the opm-autodiff library.
All that is done here is to use the pkg-config helper module and
import the configuration that was written by the CMake system (which
even may have been called earlier in the same dunecontrol "session")
Pkg-config files are written as part of the CMake configuration, and
these can be imported into AutoTools-driven projects to get the correct
compiler and linker options that has been probed.