Fix adding hwtests with multiple files.

[neobrain]

Why didn't this work before? Description ffs!

[Sonicadvance1]

Because whomever wrote it decided to describe it as a filelist, but in reality it was never designed as one.

[neobrain]

The filelist is meant to be passed as a variable like this:

set(SRCS file1.cpp file2.cpp)
add_hwtest(module SRCS)

I'm fairly sure I tested that this works, unless I'm missing something?

[Sonicadvance1]

Okay