Can't install v1.0.0 on JRuby

[ghost]

$ ruby --version
jruby 1.6.6 (ruby-1.8.7-p357) (2012-01-30 5673572) (OpenJDK 64-Bit Server VM 1.6.0_23) [linux-amd64-java]

$ gem install rcov -v '1.0.0'
Building native extensions.  This could take a while...
ERROR:  Error installing rcov:
    ERROR: Failed to build gem native extension.

        /home/zndris/.rvm/rubies/jruby-1.6.6/bin/jruby extconf.rb
WARNING: JRuby does not support native extensions or the `mkmf' library very well.
Check http://kenai.com/projects/jruby/pages/Home for alternatives.
creating Makefile

make
cc -I. -I/home/zndris/.rvm/rubies/jruby-1.6.6/lib/native/include -I/home/zndris/.rvm/rubies/jruby-1.6.6/lib/native/include/ruby -I1.8/     -fPIC  -fno-omit-frame-pointer -fno-strict-aliasing  -fexceptions    -m64 -c 1.8/callsite.c
1.8/callsite.c:2:17: fatal error: env.h: No such file or directory
compilation terminated.
make: *** [callsite.o] Error 1

Gem files will remain installed in /home/zndris/.rvm/gems/jruby-1.6.6@test/gems/rcov-1.0.0 for inspection.
Results logged to /home/zndris/.rvm/gems/jruby-1.6.6@test/gems/rcov-1.0.0/ext/rcovrt/gem_make.out

[ghost]

Duplicate of #90, sorry for the noise.