The XS modules were being built for the build platform, and the perl scripts
had build platform shebangs.
It is possible to build the XS modules by passing
PERL_EXT_CC=${stdenv.cc.targetPrefix}cc and --enable-perl-xs=yes, but they
fail to load due to a handshake key mismatch. Instead, I just decided to
disable the XS modules and use the pure Perl fallbacks when cross-compiling.
The shebangs were fixed manually using substituteInPlace.
This adds a warning to the top of each “boot” package that reads:
Note: this package is used for bootstrapping fetchurl, and thus cannot
use fetchpatch! All mutable patches (generated by GitHub or cgit) that
are needed here should be included directly in Nixpkgs as files.
This makes it clear to maintainer that they may need to treat this
package a little differently than others. Importantly, we can’t use
fetchpatch here due to using <nix/fetchurl.nix>. To avoid having stale
hashes, we need to include patches that are subject to changing
overtime (for instance, gitweb’s patches contain a version number at
the bottom).
