Fix DYNAMIC_ARCH builds with CMAKE on OSX and add corresponding test to Azure CI

[martin-frbg]

fixes #3408 using jbouny's suggestion

[isuruf]

@martin-frbg, what problem are you trying to solve here? Maybe I can help.

[martin-frbg]

@isuruf #3408 (cmake hitting the ARG_MAX on OSX when creating a DYNAMIC_ARCH library). I think I have got the hack suggested in the issue ticket converted into cmake syntax, I am just fumbling around to get the correct (cmake variable for the) library name into the custom linker command now.

[isuruf]

Ah, thanks for the pointer. How about we build the shared library using the static library instead of object files and force the user to have build the static library on macOS with gcc compiler?

[martin-frbg]

Not sure that is a "legal" or desirable way of doing it. Anyway the response file mechanism seems to work, the unsolved part is just that the library name does not appear to have been built (by system.cmake) at the time the custom linker command is executed (or more likely it is not accessible in that context).