Fix complex to not depend on C++; reimplement functions for client tests in terms of std::complex

[leekillough]

This supercedes PR# 191, which was not a full solution.

This only uses C in the hipblas.h header, unless __cplusplus is defined.

It re-implements the test functions in terms of std::complex, which has a guaranteed layout and hence reinterpret_cast<std::complex<float>&>(hipComplex) and reinterpret_cast<std::complex<double>&>(hipDoubleComplex) can be used to cast them into std::complex to use the functions in there (to avoid dependence on rocblas-complex-functions.h).

[TorreZuk]

@amcamd @daineAMD Looks fine to me, not sure what failures are expected. So Andrew and Daine can you review today as on the list of blockers. Thanks

[daineAMD]

Looks good.

[amcamd]

LGTM as long as CI tests pass

[leekillough]

It passes all tests now.

[leekillough]

The original compilation errors after template... were caused by it not recognizing C++14 code. Variable templates are not allowed in C++11. This PR does not add C++14 code; C++14 code already exists in develop. I've tried changing the language level to C++14 several ways in CMakeLists.txt, but it doesn't always work. In my GFX908 test machine, this PR builds and passes all tests.

[leekillough]

Something is different about the CI which needs investigating and fixing, which is causing those build failures. I can't reproduce them locally. The C++ code is fine; the errors, as with nearly all C++ template compilation errors, are misleading. It looks like the CI compiler is not picking up -std=c++14 even though it's specified in CMakeLists.txt.

To reproduce the failures on my own machine, I would need the right Docker container.