rewrite Linux nodatacow use in pure Perl w/o system
btrfs is Linux-only at the moment (and likely to remain that way
for practical purposes). So rely on Linux ABI stability and use
the `syscall' and `ioctl' perlops rather than relying on Inline::C.
Inline::C (and gcc||clang) are monstrous dependencies which we
can't expect users to have.
This makes supporting new architectures more difficult, but new
architectures come along rarely and this reduces the burden for
the majority of Linux users on popular architectures (while
still avoiding the distribution of pre-built binaries).
Link: https://public-inbox.org/meta/YbCPWGaJEkV6eWfo@codewreck.org/