Remove architecture check from CMake package

[mmha]

Description

CMake adds an architecture check to each package by default. This causes the package to break if e. g. the package was built on a 32 bit system and used on a 64 bit system, even though this is a header-only library. This can happen if a caching package manager like conan is being used.

In CMake 3.14 this check can be disabled by passing ARCH_INDEPENDENT to write_basic_package_version_file. In versions prior to that CMAKE_SIZEOF_VOID_P needs to be unset for the duration of this function.

GitHub Issues

catchorg/Catch2#1368

[onqtam]

Thanks!

[Morwenn]

Is this something that happens despite specifying header_only in package_info in the conanfile?

[mmha]

This happens because specifying header_only in package_info.

When stating to conan that it's a header-only lib, you're telling conan that you can reuse the built package for all architectures and OSes.

The docs say this:

That means, if someone consumes MyLib with the header_only=True option, the package downloaded and used will be the same, irrespective of the OS, compiler or architecture the consumer is building with.

But the CMake write_basic_package_version_file does add a platform check, which makes CMake install()ed header-only libs platform-dependent unless worked around (which is what this PR did).

[Morwenn]

Nice & concise explanation, thank you very much!