ifort apparently does not return complex numbers in registers as in C/C++ (or gfortran), but instead creates a "hidden" first parameter for the return value. The option --complex-return=gnu|intel has been added, as well as a guess based on a provided FC if not specified (otherwise default to gnu). This option affects the signatures of cdotc, cdotu, zdotc, and zdotu, and a single library cannot be used with both GNU and Intel Fortran compilers. Fixes #433.