The 'undefined reference' means that the library that resolves that symbol has not been located.
In the Makefile.PL there's a line:

my $cc = join(" ", $Config{cc}, $libs, @ccflags, "-l${lib}", "-o", $ex
+e, (map { "-I$_" } @incs), "test_js.c");
[download]

It would be helpful if you could insert a print "$cc\n"; into that Makefile.PL and re-run it again so we can see just what that command ($cc) actually is.
I think that ${lib} in the above command is set to 'js', so 'libjs.a' or 'js.a' or 'js.lib' needs to be found. Is there such a file in in $ENV{JS_LIB} ?

Cheers,
Rob