Trouble with initial rails gem install on OSX 10.9 Mavericks -

after little hastle have rbenv , ruby installed. when try install rails, i'm failing here:

$ gem install rails -v 4.2.3  [....]  checking main() in -llzma... yes checking xmlparsedoc() in libxml/parser.h... no checking xmlparsedoc() in -lxml2... no checking xmlparsedoc() in -llibxml2... no ----- libxml2 missing.  please locate mkmf.log investigate how failing. ----- *** extconf.rb failed *** not create makefile due reason, lack of necessary libraries and/or headers.  check mkmf.log file more details.  may need configuration options.  [....] 

i use macports package management , seems libxml2 present (as expect be):

$ port list *libxml* libxml                         @1.8.17         textproc/libxml libxml2                        @2.9.2          textproc/libxml2 libxmldiff                     @0.2.5          textproc/libxmldiff libxmlxx                       @1.0.5          textproc/libxmlxx libxmlxx2                      @2.38.1         textproc/libxmlxx2 p5-libxml-enno                 @1.20.0         perl/p5-libxml-enno p5-libxml-perl                 @0.80.0         perl/p5-libxml-perl p5-xml-libxml                  @2.12.300       perl/p5-xml-libxml p5-xml-libxml-simple           @0.950.0        perl/p5-xml-libxml-simple p5-xml-rss-libxml              @0.310.500      perl/p5-xml-rss-libxml p5.16-libxml-enno              @1.20.0         perl/p5-graveyard p5.16-libxml-perl              @0.80.0         perl/p5-graveyard p5.16-xml-libxml               @2.12.300       perl/p5-graveyard p5.16-xml-libxml-simple        @0.950.0        perl/p5-graveyard p5.16-xml-rss-libxml           @0.310.500      perl/p5-graveyard p5.18-libxml-enno              @1.20.0         perl/p5-graveyard p5.18-libxml-perl              @0.80.0         perl/p5-graveyard p5.18-xml-libxml               @2.12.300       perl/p5-graveyard p5.18-xml-libxml-simple        @0.950.0        perl/p5-graveyard p5.18-xml-rss-libxml           @0.310.500      perl/p5-graveyard p5.20-libxml-enno              @1.20.0         perl/p5-graveyard p5.20-libxml-perl              @0.80.0         perl/p5-graveyard p5.20-xml-libxml               @2.12.300       perl/p5-graveyard p5.20-xml-libxml-simple        @0.950.0        perl/p5-graveyard p5.20-xml-rss-libxml           @0.310.500      perl/p5-graveyard p5.22-libxml-enno              @1.20.0         perl/p5-libxml-enno p5.22-libxml-perl              @0.80.0         perl/p5-libxml-perl p5.22-xml-libxml               @2.12.300       perl/p5-xml-libxml p5.22-xml-libxml-simple        @0.950.0        perl/p5-xml-libxml-simple p5.22-xml-rss-libxml           @0.310.500      perl/p5-xml-rss-libxml py-libxml2                     @2.9.2          python/py-libxml2 py24-libxml2                   @2.9.2          python/py-graveyard py25-libxml2                   @2.9.2          python/py-graveyard py26-libxml2                   @2.9.2          python/py-graveyard py27-libxml2                   @2.9.2          python/py-libxml2 py34-libxml2                   @2.9.2          python/py-libxml2 py35-libxml2                   @2.9.2          python/py-libxml2 rb-libxml2                     @2.3.4          ruby/rb-libxml2 

try installing as:

gem install rails -v 4.2.3 -- --use-system-libraries