Allow AR to be set in the environment

[orlitzky]

The AR variable (like CC or LD) may be set by the user in her environment. In https://github.com/xianyi/OpenBLAS/blob/develop/Makefile.system#L266 however, it is set unconditionally, making the value in the Makefile difficult to override. I would suggest using the conditional assignment operator ?= instead of =. That way the Makefile only sets it if it's not already set.

I'm able to work around this another way but it may be nice for everyone else =)

It was reported to us at https://bugs.gentoo.org/725608

[martin-frbg]

Interesting, guess there have not been that many alternate implementations of ar in the past ~15 years that did not also hijack the name "ar" system-wide. Guess the same applies to AS, LD and RANLIB there (and I believe nothing actually uses NM)

[orlitzky]

Yes, the others should probably be conditionally defined as well. I know AS is a standard name, that RANLIB is used by automake, and that and LD is used by e.g. the linux kernel, so people may try to override those. Even if no one is going to complain about them I don't see the harm in conditionally defining them, just in case.

[orlitzky]

It looks like meson has also added support for LD in the environment: mesonbuild/meson#6207

That grants a bit more validity to the expectation that setting LD in the environment will override the linker used.

[brada4]

Also AR=${{C|F}C} could work.

[orlitzky]

Thank you!