Fix superlu and quadmath

superLU did not work for me (I compile it myself and use the internal BLAS library), the quadmath test did not include the "CHECK_C_SOURCE_COMPILES" macro which it uses. This made both tests fail for me even if the correct version of the libraries were present. (Although I'm not sure what went on with the quadmath test since I'm sure that it worked for me when I wrote it...)