[feature] Option to set default profile:build and profile:host in conanfile

Summary Can we get an option to specify a default profile:build and profile:host in the conanfile?

Nice to haves:

• Allow for profile:build to use a variable for the current architecture (eg, so it will use a linux_x64 profile if you’re on a linux_x64 machine)
• Allow a ‘none’ value for profile:host, so that the user is forced to enter a value on the commandline.
• Allow values specified as command line args to override defaults specified in conanfile

Justification: On firmware projects that require cross-compilation, profile:build is generally going to be the current architecture of the machine the developer is using, and profile:host will almost always be the embedded device architecture (eg, an ARM toolchain).

Given that omitting profile:build and profile:host from the commandline makes significant changes to the build, I feel like this would end up being a common pitfall when getting new developers up to speed on a conan project. I think it would be less confusing if I could specify default values in the conanfile, but still be able to override them as needed.

• I’ve read the CONTRIBUTING guide.

[db4]

@solvingj I never knew that settings could be specified this way for individual packages. That’s exactly what I need, thanks a lot!

[solvingj]

I’m pretty novice on the cross-build implications. Would it work to add this to the settings of your build_profile?

    [settings]
    cmake:arch=x86_64
    cmake:build_type=Release