Handle CC_FOR_BUILD and CXX_FOR_BUILD where they are used but not actually set

[barracuda156]

There were several cases of ports being broken by careless usage of CC_FOR_BUILD and/or CXX_FOR_BUILD while those were not set to anything. In result, Macports compiler settings get ignored, and a system default compiler is picked or even some random one. That cannot work correctly. What we actually need it that the right compiler is picked for the build.

Can this be fixed in the base instead of per-port patches?

[ryandesign (Ryan Carsten Schmidt)]

As far as I know it is not a widespread problem because not many build systems use CC_FOR_BUILD or CXX_FOR_BUILD. Today I see only 18 portfiles mentioning the former and 1 setting the latter. However it might be nice to handle it centrally.

Presumably what you want is for new options configure.cc_for_build and configure.cxx_for_build to be introduced. These would default to ${configure.cc} and ${configure.cxx}. The CC_FOR_BUILD and CXX_FOR_BUILD environment variables would be set to ${configure.cc_for_build} and ${configure.cxx_for_build}.

I see a couple ports (gtk3, gtk3-devel, fossil) including the -arch flag. I would guess that should not be done because the whole point of these env vars is to specify a compiler that builds things for the build machine and it should do so without needing to be told what arch to do it for, and especially if you are, for example, on an x86_64 machine building for arm64, then you do not want -arch arm64 to be used to compile things that will need to run on the x86_64 build machine.

[kencu (Ken)]

meson, in particular, uses CC_FOR_BUILD and CXX_FOR_BUILD when cross-compiling.

​https://mesonbuild.com/Cross-compilation.html

​https://mesonbuild.com/Reference-tables.html#environment-variables-per-machine

[ryandesign (Ryan Carsten Schmidt)]

That could at least be handled by the meson portgroup. That prompted me to check the portgroups. At the moment, only the muniversal 1.1 portgroup sets them. It also deals with CFLAGS_FOR_BUILD, CPPFLAGS_FOR_BUILD, CXXFLAGS_FOR_BUILD, and LDFLAGS_FOR_BUILD. I'm not sure who uses those or what we should put in there by default, if we added support for those to base as well.