The historical assumption of compilation is that the platform where the code is compiled will be the same as the platform where the final code will be executed (if not literally the same machine, then at least one that is CPU and ABI compatible at the operating system level). This is a reasonable assumption for most desktop projects; However, for mobile platforms, this isn't the case.
On mobile platforms, an app is compiled on a desktop platform, and transferred to the mobile device (or a simulator) for testing. The compiler is not executed on device. Therefore, it must be possible to build a binary artefact for a CPU architecture and a ABI that is different the platform that is running the compiler.
A microcosm of this problem exists on macOS as a result of the Apple Silicon transition. Most CI systems don't provide native ARM hardware, but most developers will still want ARM64-compatible build artefacts. Apple has provided the tools compile fat binaries on x86_64 hardware; however, in this case, the host platform (macOS on x86_64) will still be one of the outputs of the compilation process. For mobile platforms, the computer that compiles the code will not be able to execute the code that has been compiled.
Compiler and build toolchains (e.g., autoconf/automake) have long supported cross-compilation; however, these cross-compilation capabilities are easy to break unless they are exercised regularly.
In the Python space, tools like crossenv
also exist; these tools use a collection of path hacks and overrides of known
sources of platform-specific details (like distutils) to provide a
cross-compilation environment. However, these solutions tend to be somewhat
fragile as aren't first-class citizens of the Python ecosystem.