linux: Fix STATFS_IS_STATFS64 definition

aarch64, arc, ia64, mips64, powerpc64, riscv32, riscv64, s390x, sparc64,
and x86_64 defines STATFS_IS_STATFS64 to 0, but all of them alias
statfs to statfs64 and the struct statfs has the same and layout of
struct statfs64.

The correct definition will be used on the [f]statfs[64] consolidation.

This patch does not change code generation since the symbols are
implemented using the auto-generation syscall for all the aforementioned
ABIs.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>