Build problem on OS X 10.5 - ruby

With default ./configure, clearsilver 0.10.5 won't build.

Workaround is to --disable-ruby.

# ./configure
...
checking for ruby... found /usr/bin/ruby
...
/usr/bin/ruby install.rb config -- --with-hdf-include=../../..
--with-hdf-lib=../../../libs --make-prog=make
install.rb: entering config phase...
---> lib
<--- lib
---> ext
---> ext/hdf
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
/Users/toby/clearsilver-0.10.5/ruby/ext/hdf/extconf.rb
--with-hdf-include=../../.. --with-hdf-lib=../../../libs --make-prog=make
checking for deflate() in -lz... yes
checking for ClearSilver.h... yes
checking for hdf_init() in -lneo_utl... no
*** /Users/toby/clearsilver-0.10.5/ruby/ext/hdf/extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=/Users/toby/clearsilver-0.10.5/ruby/ext/hdf
        --curdir
       
--ruby=/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
        --with-hdf-dir
        --without-hdf-dir
        --with-hdf-include=${hdf-dir}/include
        --with-hdf-lib=${hdf-dir}/lib
        --with-zlib
        --without-zlib
        --with-neo_utllib
        --without-neo_utllib
config failed
'system
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby
/Users/toby/clearsilver-0.10.5/ruby/ext/hdf/extconf.rb
--with-hdf-include=../../.. --with-hdf-lib=../../../libs
--make-prog=make' failed
try 'ruby install.rb --help' for usage
make[1]: *** [config.save] Error 1
make: *** [cs] Error 2