Fix add_cmake_flag in cmake helper

[blastrock]

Changelog: Bugfix: Fixes a bug in the CMake build helper about how flags are appended
Docs: omit

The description of the add_cmake_flags function does not correspond to the actual behavior.

[CLAassistant]

All committers have signed the CLA.

[memsharded]

Hi @blastrock

Thanks very much for fixing this, indeed seems a bug. Just two things:

• Could you please check the CLA link above? It seems you didn't sign it, or you used a different email for the commit than your github user one.

• If this was a bug, and it went undetected, it is clearly missing a test. Could you please try to provide a test that covers this case? Ask for help, or tell, and we would try to contribute that test, but definitely should be tested.

Thanks again!

[blastrock]

Hi,

I just signed the CLA.

Sorry, I probably won't have time for the test. According to the file (which contains the only usages of the function), the only case where we add two flags (and may thus trigger a bug) is when using parallel build with MSVC, so the test should target that. Also, arch_flag seems to be added twice, not sure if that's intended.

I randomly stumbled upon the latent bug while reading the source and just wanted to report it :)

[memsharded]

I happens that it is not possible to force that bug in a test. Fortunately, this shouldn't be affecting anyone. Appending calling add_cmake_flag() never happens, as it is mutually exclusive the case for parallel + VS and the case of arch (-mXX, by gcc, clang).

So I am merging it now, as it is an improvement anyway that could protect in the future. Thanks!

@lasote, if this is not actually used, should we refactor it?