Unify generated libc platform bindings

[ardera]

now that the generated libc platform bindings are portable (i.e. the same for each ABI, so linux-armhf, arm64, i386 and amd64), the old boilerplate code that was there to wrap the platform-specific bindings and provide a common API can be deleted and we can just use the bindings that are generated for amd64 (for example).

Though we should still generate the bindings for all platforms and check whether they are the same, so for example we catch outliers such as O_NOFOLLOW and O_DIRECTORY, which have different values depending on ABI.