Allow for either px or ix dolphin in builds

Closes #422

See merge request !413

Models and cdsrfm need dolphin symvers.  The code needs to look for either ix or px dolphin symvers.

We are assuming we would never have both installed, but in that case, the goal is to have px files overwrite ix files.

find_module_symvers has been changed to look for multiple module names.  It will return all symvers found among all the models.

RCG: avx demod parts added

See merge request !409

Some code in the demod rotation calcs was compiled with the assumption that %rax was preserved across a call to sincos.
This is not the case.  Now sincos saves %rax on the stack.