As I understand things, the module needs to be loaded for the ./Build step, but you are loading it during the perl Build.PL step. I think the following will do the trick:

my $class = Module::Build->subclass(code => <<'EOF');
sub ACTION_build {
   require Parse::RecDescent;
   ...
}
EOF
[download]

I think this will also work:

my $class = Module::Build->subclass(code => <<'EOF');
use Parse::RecDescent;
sub ACTION_build {
   ...
}
EOF
[download]