use ExtUtils::Liblist;

my @vars = ExtUtils::Liblist->ext( '-L/sw/lib -ltidy', 0, 1 );
my $libs = $vars[2];

WriteMakefile(
    NAME                => 'HTML::Tidy',
    # ...

    LIBS                => [$libs],
    NEEDS_LINKING       => 1,
    INC                 => '-I. -I/usr/include/tidy -I/usr/local/include/tidy -I/sw/include/tidy',

    EXE_FILES           => [qw(bin/webtidy)],
);