use CXX/CC environment variables to set the compiler commands

[HLinde]

Hi!

For the build process on conda-forge the issue came up, that conda-forge actually provides the compiler that should be used for packaging via the CXX environment variable. See also the discussion

I can build the packages now by applying a patch before building, but maybe you want to take over that behaviour instead?
It only affects the "make" based build on Linux when I test if Go4 can run Go4ExampleSimple and Go4ExampleUserSource. It's not necessary for building Go4 itself with CMake.

The previous setting to g++/clang++ is now the fallback default value.

[linev]

Since several years we recommend to use cmake for go4 compilation.
Also for all examples we provide cmake files.

I see no problem to merge PR.
The only I am curios of - how far to the past syntax like CXX ?= g++ supported by makefiles?

[HLinde]

Ok, thank you! But then I should maybe also add a test for cmake compilation of the user analysis.

The syntax is apparently possible since make Version 3.77, from the NEWS file of that version:

• Implement BSD make's "?=" variable assignment operator. The variable
  is assigned the specified value only if that variable is not already
  defined.

[linev]

The syntax is apparently possible since make Version 3.77, from the NEWS file of that version:

So it pretty old feature

[linev]

But then I should maybe also add a test for cmake compilation of the user analysis.

Yes, you can do it as well.
But all analyses examples compiled by default with go4.

[HLinde]

Ah, sorry it was not clear what I'm using the examples for.
I copied them to another folder in order to test building and running an analysis as a "user" after installing the package.
So now I test one example with make and one example with cmake:
https://github.com/conda-forge/staged-recipes/pull/30301/files#diff-12195140c17f424408007f926c586e559c38213864b882f2aa99b39c4adeef13
(This script is running in a virtual environment that has the package installed after the packaging finished.)

[linev]

Yes, this is also valid approach.

I expect most of user analysis using old Makefiles - so one need to properly support them.

Grate that you are doing this