dsp/benchmark/magnitude_power_uc8_benchmark.c is missing an include for math.h

[gtjoseph]

...which causes lots of errors like...

In file included from dsp/generated/benchmark.c:1249:
dsp/generated/../benchmark/magnitude_power_uc8_benchmark.c: In function ‘starch_magnitude_power_uc8_benchmark’:
dsp/generated/../benchmark/magnitude_power_uc8_benchmark.c:20:36: error: implicit declaration of function ‘cos’ [-Werror=implicit-function-declaration]
   20 |         in[i].I = (uint8_t) (0.9 * cos(degrees * M_PI / 180.0) * 128 + 127.4);
      |                                    ^~~

[mutability]

Hmm, I think this is being masked by an ordering thing. On a clean checkout this works because another benchmark which does include math.h is included first.