LWP doesn't cross compile

[exarkun]

Issue description

these derivations will be built:
  /nix/store/2v67jkp101pdz1bihd097r81hwvdmbg6-perl5.28.0-libwww-perl-6.35-armv7l-unknown-linux-gnueabihf.drv
building '/nix/store/2v67jkp101pdz1bihd097r81hwvdmbg6-perl5.28.0-libwww-perl-6.35-armv7l-unknown-linux-gnueabihf.drv'...
unpacking sources
unpacking source archive /nix/store/xdrlwhhv83spwl2qfgfzya1jwgh8bdlz-libwww-perl-6.35.tar.gz
source root is libwww-perl-6.35
setting SOURCE_DATE_EPOCH to timestamp 1531716538 of file libwww-perl-6.35/xt/release/changes_has_content.t
patching sources
updateAutotoolsGnuConfigScriptsPhase
configuring
patching ./bin/lwp-mirror...
patching ./bin/lwp-request...
patching ./bin/lwp-download...
patching ./bin/lwp-dump...
patching ./t/00-report-prereqs.t...
patching ./xt/author/net/cgi-bin/slowread...
patching ./xt/author/net/cgi-bin/timeout...
patching ./xt/author/net/cgi-bin/nph-slowdata...
patching ./xt/author/net/cgi-bin/moved...
patching ./xt/author/net/cgi-bin/test...
patching ./xt/author/minimum-version.t...
patching ./xt/author/mojibake.t...
patching ./xt/author/pod-syntax.t...
patching ./xt/author/misc/dbmrobot...
patching ./xt/author/misc/get-callback...
patching ./xt/author/misc/get-file...
patching ./xt/author/pod-coverage.t...
patching ./talk-to-ourself...
Can't load module B, dynamic loading not available in this perl.
  (You may need to build a new perl executable which either supports
  dynamic loading or has the B module statically linked into it.)
 at /nix/store/7c31x2idh9fkc0iawyyvrdxxwd1xnfn6-perl-5.28.0-armv7l-unknown-linux-gnueabihf/lib/perl5/5.28.0/armv7l-linux/B.pm line 33.
BEGIN failed--compilation aborted at /nix/store/7c31x2idh9fkc0iawyyvrdxxwd1xnfn6-perl-5.28.0-armv7l-unknown-linux-gnueabihf/lib/perl5/5.28.0/armv7l-linux/B.pm line 33.
Compilation failed in require at /nix/store/7c31x2idh9fkc0iawyyvrdxxwd1xnfn6-perl-5.28.0-armv7l-unknown-linux-gnueabihf/lib/perl5/5.28.0/CPAN/Meta/Requirements.pm line 90.
builder for '/nix/store/2v67jkp101pdz1bihd097r81hwvdmbg6-perl5.28.0-libwww-perl-6.35-armv7l-unknown-linux-gnueabihf.drv' failed with exit code 255
error: build of '/nix/store/2v67jkp101pdz1bihd097r81hwvdmbg6-perl5.28.0-libwww-perl-6.35-armv7l-unknown-linux-gnueabihf.drv' failed

Steps to reproduce

$ cat libwww.nix
#!/bin/sh
nix-build -E 'let pkgs = import <nixpkgs> { crossSystem = { system = "armv7l-linux"; }; }; in pkgs.perlPackages.LWP'
$ bash libwww.nix

Technical details

$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 4.15.0-36-generic, Ubuntu, 18.04.1 LTS (Bionic Beaver)`
 - multi-user?: `no`
 - sandbox: `no`
 - version: `nix-env (Nix) 2.0.4`
 - channels(exarkun): `"nixpkgs-18.09.1228.a4c4cbb613c"`
 - nixpkgs: `/home/exarkun/.nix-defexpr/channels/nixpkgs`