Fix a bunch of ODR violations.

• indexed_view.cpp:
  • IndexPair conflicts with the version in TensorMeta.
  • <valarray> has limited use here, and contains a min() call that conflicts with the macro in main.h
• packetmath.cpp/packetmath_test_shared.h:
  • explicitly defining pxor, pandnot and por for these float types leads to explicit specializations after instantiations, since they are used elsewhere first. Not sure what the purpose is, since tests seem to pass without these.
• TensorGlobalFunctions.h:
  • betainc clashes with the one in SpecialFunctionsArrayAPI.h, we need to explicitly specialize for TensorBase.