HTML::Parser on older perl versions

I maintain some CPAN modules that use libwww-perl.  I'd like to have my
modules work on any perl back to v5.6.0, but in testing I'm finding that
HTML::Parser itself won't go back that far.

With perl v5.8.0 I get this when building:

cc -c   -D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O3   -DVERSION=\"3.56\" -DXS_VERSION=\"3.56\" -fPIC "-I/home/zefram/usr/perl/perl_install/perl-5.8.0-i32-f52/lib/5.8.0/i386-linux-thread-multi/CORE"  -DMARKED_SECTION Parser.c
Parser.xs: In function `dup_pstate':
Parser.xs:290: error: `CLONEf_JOIN_IN' undeclared (first use in this function)
Parser.xs:290: error: (Each undeclared identifier is reported only once
Parser.xs:290: error: for each function it appears in.)
make: *** [Parser.o] Error 1

With perl v5.6.0 it builds OK, but one of the tests fails:

t/headparser........./\x{FEFF}/: Can't use \x{} without 'use utf8' declaration at /home/zefram/usr/perl/perl_install/perl-5.6.0-i32-f52/cpan/build/HTML-Parser-3.56/blib/lib/HTML/HeadParser.pm line 211.
Compilation failed in require at t/headparser.t line 83.
# Looks like your test died before it could output anything.
t/headparser.........dubious                                                 
        Test returned status 255 (wstat 65280, 0xff00)
DIED. FAILED tests 1-11
        Failed 11/11 tests, 0.00% okay

It works fine on v5.6.1 and v5.6.2.

-zefram