It's a runtime requirement of Pod::Wordlist, which includes this code:

use constant {

        MAXWORDLENGTH => 50,

        _DIST_DIR => do {
                my $dir;
                if ( -e __FILE__ ) {
                        my $local_dir = path(__FILE__)->parent->parent->parent->child('share/dist/Pod-Spell');
                        $dir = $local_dir->absolute if -e $local_dir;
                }
                if ( not defined $dir ) {
                        require File::ShareDir;
                        $dir = File::ShareDir::dist_dir('Pod-Spell');
                }
                "$dir"
        },
};

The dependency isn't automatically picked up (and I wouldn't expect it to be), and the lack of it causes failures like this:

$ make test TEST_POD=1
PERL_DL_NONLAZY=1 "/usr/bin/perl" "-MExtUtils::Command::MM" "-MTest::Harness" "-e" "undef *Test::Harness::Switches; test_harness(0, 'inc', 'blib/lib', 'blib/arch')" t/*.t xt/*.t
t/00_compile.t ....... ok
t/01_basic.t ......... ok
t/02_default.t ....... ok
t/03_builder.t ....... ok
xt/01_pod.t .......... ok
xt/02_podcoverage.t .. ok
Can't locate File/ShareDir.pm in @INC (you may need to install the File::ShareDir module) (@INC contains: /builddir/build/BUILD/MouseX-ConfigFromFile-0.05/inc /builddir/build/BUILD/MouseX-ConfigFromFile-0.05/blib/lib /builddir/build/BUILD/MouseX-ConfigFromFile-0.05/blib/arch /usr/local/lib/perl5 /usr/local/share/perl5 /usr/lib/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib/perl5 /usr/share/perl5 .) at /usr/share/perl5/vendor_perl/Pod/Wordlist.pm line 24.
BEGIN failed--compilation aborted at /usr/share/perl5/vendor_perl/Pod/Wordlist.pm line 29.
Compilation failed in require at /usr/share/perl5/vendor_perl/Pod/Spell.pm line 15.
# Looks like your test exited with 2 before it could output anything.
xt/03_podspell.t ..... 
Dubious, test returned 2 (wstat 512, 0x200)
Failed 1/1 subtests 
Test Summary Report
-------------------
xt/03_podspell.t   (Wstat: 512 Tests: 0 Failed: 0)
  Non-zero exit status: 2
  Parse errors: Bad plan.  You planned 1 tests but ran 0.
Files=7, Tests=19,  3 wallclock secs ( 0.10 usr  0.03 sys +  2.92 cusr  0.24 csys =  3.29 CPU)
Result: FAIL
Failed 1/7 test programs. 0/19 subtests failed.
Makefile:781: recipe for target 'test_dynamic' failed

This is currently causing the following packages of mine to FTBFS:
perl-B-Hooks-EndOfScope
perl-CPAN-Meta-Requirements
perl-MouseX-ConfigFromFile
perl-MouseX-Types-Path-Class
perl-Package-DeprecationManager
perl-Perl-OSType
perl-Test-Assert
... and several others