Exported-symbol changes in 5.13

Sometimes one hits issues with macros that use inlined functions that have different EXPORT_SYMBOL behaviour on different architectures. For example, get_user() on powerpc was recently changed [1] to access mmu_feature_keys[] that is now an EXPORT_SYMBOL_GPL symbol. So some out of tree non-GPL'd kernel modules now fail to build because of this on a specific architecture. I don't believe there are any sanity checks on the kernel to check for these inconsistencies.

[1] 7613f5a66becfd0e43a0f34de8518695888f5458 ("powerpc/64s/kuap: Use mmu_has_feature()")