http://stackoverflow.com/questions/37933375/how-to-build-a-ruby-gem-using-nix-that-has-native-extensions

$ nix-build 2>&1

these derivations will be built:
  /nix/store/2jw5z62h038w6zjann9cw2jj8gdmr3s3-ruby2.3.1-p0-rails-deprecated_sanitizer-1.0.3.drv
  /nix/store/4w133lxvpwhrj39lhwkghsmnx1mgw96a-ruby2.3.1-p0-rails-dom-testing-1.0.7.drv
  /nix/store/7nni4gl2w0ms651kh6davpm2w7lc66km-ruby2.3.1-p0-rack-test-0.6.3.drv
  /nix/store/b1qim6zsqwqmfig0vvwwfrkaxhq8ryl2-ruby2.3.1-p0-spring-1.7.1.drv
  /nix/store/b247cvywv3pgic1llfz6w0bpmpyjxydf-ruby2.3.1-p0-sprockets-3.6.1.drv
  /nix/store/b6vbxqdd38xawvv8mbzmbhda4kki6wjc-ruby2.3.1-p0-thread_safe-0.3.5.drv
  /nix/store/bl4ndhd0ia08vsf6xj3vz7a03p361vik-ruby2.3.1-p0-sprockets-rails-3.0.4.drv
  /nix/store/cr4d4gyqyhh03a2ibpqyfarpi7wab9b6-ruby2.3.1-p0-rake-11.2.2.drv
  /nix/store/gdr336rfjcjf0yrpkb5ska955af9nw8l-ruby2.3.1-p0-rack-1.6.4.drv
  /nix/store/gl7sp7izhlrh33pvykjghfjjxz1c67z6-ruby2.3.1-p0-railties-4.2.6.drv
  /nix/store/imk4jyi0iys9v4pbq4gdlznq78g4c9c6-ruby2.3.1-p0-nokogiri-1.6.8.drv
  /nix/store/lv3vcfyi55iiznnjfa5vrxnvrw4yif9n-ruby2.3.1-p0-web-console-2.3.0.drv
  /nix/store/m9m1vd3jhnl5a1z65i0jcv94na2dxg0y-ruby2.3.1-p0-tzinfo-1.2.2.drv
  /nix/store/sadjciicgd9ghi7582yg7v8ap4vbfgy9-ruby2.3.1-p0-rails-4.2.6.drv
  /nix/store/sdxkwaw7prff2jip8mna8m3gb9xxc59r-ruby2.3.1-p0-pkg-config-1.1.7.drv
  /nix/store/xn1pg054b8licqf8vzhd161h2hw6yn8d-ruby2.3.1-p0-rails-html-sanitizer-1.0.3.drv
  /nix/store/gh0j7m97r9cbayw1b9racjc48yzibsam-novallio-blog-0.0.1-gems.drv
  /nix/store/7jdqmb13vcip2ka5lcvw9pkx1m4s5jzg-novallio-blog-0.0.1.drv
building path(s) ‘/nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8’
unpacking sources
patching sources
installing
buildFlags: --use-system-libraries --with-zlib-dir=/nix/store/dn9l2kd6ai731k34pzlzr5dz3in0rn31-zlib-1.2.8-dev --with-xml2-lib=/nix/store/9w15hz68wz5qnihfhsbr281d0sfs20a8-libxml2-2.9.3/lib --with-xml2-include=/nix/store/rq94vzxa92p30prfgv9jz83xiy8hkn2k-libxml2-2.9.3-dev/include/libxml2 --with-xslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-xslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include --with-exslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-exslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include
WARNING:  You build with buildroot.
  Build root: /
  Bin dir: /nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8/lib/ruby/gems/2.3.1/bin
  Gem home: /nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8/lib/ruby/gems/2.3.1
Building native extensions with: '--use-system-libraries --with-zlib-dir=/nix/store/dn9l2kd6ai731k34pzlzr5dz3in0rn31-zlib-1.2.8-dev --with-xml2-lib=/nix/store/9w15hz68wz5qnihfhsbr281d0sfs20a8-libxml2-2.9.3/lib --with-xml2-include=/nix/store/rq94vzxa92p30prfgv9jz83xiy8hkn2k-libxml2-2.9.3-dev/include/libxml2 --with-xslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-xslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include --with-exslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-exslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include'
This could take a while...
ERROR:  Error installing /nix/store/y8wf8kjaqqkkdbcwra3y5027kxi4bw4b-nokogiri-1.6.8.gem:
	ERROR: Failed to build gem native extension.

    current directory: /nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8/lib/ruby/gems/2.3.1/gems/nokogiri-1.6.8/ext/nokogiri
/nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/bin/ruby -r ./siteconf20160620-26514-7qjbro.rb extconf.rb --use-system-libraries --with-zlib-dir=/nix/store/dn9l2kd6ai731k34pzlzr5dz3in0rn31-zlib-1.2.8-dev --with-xml2-lib=/nix/store/9w15hz68wz5qnihfhsbr281d0sfs20a8-libxml2-2.9.3/lib --with-xml2-include=/nix/store/rq94vzxa92p30prfgv9jz83xiy8hkn2k-libxml2-2.9.3-dev/include/libxml2 --with-xslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-xslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include --with-exslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-exslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include
*** 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=.
	--curdir
	--ruby=/nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/bin/$(RUBY_BASE_NAME)
/nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/lib/ruby/site_ruby/2.3.0/rubygems/dependency.rb:321:in `to_specs': Could not find 'pkg-config' (~> 1.1.7) among 5 total gem(s) (Gem::LoadError)
Checked in 'GEM_PATH=/nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/lib/ruby/gems/2.3.0:/nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8/lib/ruby/gems/2.3.1', execute `gem env` for more information
	from /nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/lib/ruby/site_ruby/2.3.0/rubygems/dependency.rb:330:in `to_spec'
	from /nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_gem.rb:65:in `gem'
	from extconf.rb:112:in `<main>'

extconf failed, exit code 1

Gem files will remain installed in /nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8/lib/ruby/gems/2.3.1/gems/nokogiri-1.6.8 for inspection.
Results logged to /nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8/lib/ruby/gems/2.3.1/extensions/x86_64-linux/2.3.0/nokogiri-1.6.8/gem_make.out
builder for ‘/nix/store/imk4jyi0iys9v4pbq4gdlznq78g4c9c6-ruby2.3.1-p0-nokogiri-1.6.8.drv’ failed with exit code 1
cannot build derivation ‘/nix/store/gh0j7m97r9cbayw1b9racjc48yzibsam-novallio-blog-0.0.1-gems.drv’: 1 dependencies couldn't be built
cannot build derivation ‘/nix/store/7jdqmb13vcip2ka5lcvw9pkx1m4s5jzg-novallio-blog-0.0.1.drv’: 1 dependencies couldn't be built
error: build of ‘/nix/store/7jdqmb13vcip2ka5lcvw9pkx1m4s5jzg-novallio-blog-0.0.1.drv’ failed

correct configure

 $ cd /nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8/lib/ruby/gems/2.3.1/gems/nokogiri-1.6.8/ext/nokogiri
 $ /nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/bin/ruby extconf.rb --use-system-libraries --with-zlib-dir=/nix/store/dn9l2kd6ai731k34pzlzr5dz3in0rn31-zlib-1.2.8-dev --with-xml2-lib=/nix/store/9w15hz68wz5qnihfhsbr281d0sfs20a8-libxml2-2.9.3/lib --with-xml2-include=/nix/store/rq94vzxa92p30prfgv9jz83xiy8hkn2k-libxml2-2.9.3-dev/include/libxml2 --with-xslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-xslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include --with-exslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-exslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include
Using pkg-config version 1.1.7
checking if the C compiler accepts ... yes
Building nokogiri using system libraries.
checking for xmlParseDoc() in libxml/parser.h... no
checking for xmlParseDoc() in -lxml2... yes
checking for xsltParseStylesheetDoc() in libxslt/xslt.h... no
checking for xsltParseStylesheetDoc() in -lxslt... yes
checking for exsltFuncRegister() in libexslt/exslt.h... no
checking for exsltFuncRegister() in -lexslt... yes
checking for xmlHasFeature()... yes
checking for xmlFirstElementChild()... yes
checking for xmlRelaxNGSetParserStructuredErrors()... yes
checking for xmlRelaxNGSetParserStructuredErrors()... yes
checking for xmlRelaxNGSetValidStructuredErrors()... yes
checking for xmlSchemaSetValidStructuredErrors()... yes
checking for xmlSchemaSetParserStructuredErrors()... yes
creating Makefile

exact manual configure

 $ cd /nix/store/z26mymfryhqqh7y8w94qr0xc88q46dvr-ruby2.3.1-p0-nokogiri-1.6.8/lib/ruby/gems/2.3.1/gems/nokogiri-1.6.8/ext/nokogiri
 $ /nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/bin/ruby -r ./siteconf20160620-11206-1hntp6t.rb extconf.rb --use-system-libraries --with-zlib-dir=/nix/store/dn9l2kd6ai731k34pzlzr5dz3in0rn31-zlib-1.2.8-dev --with-xml2-lib=/nix/store/9w15hz68wz5qnihfhsbr281d0sfs20a8-libxml2-2.9.3/lib --with-xml2-include=/nix/store/rq94vzxa92p30prfgv9jz83xiy8hkn2k-libxml2-2.9.3-dev/include/libxml2 --with-xslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-xslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include --with-exslt-lib=/nix/store/fv137j5wxp4dg1wjqdbk8i2l087163b7-libxslt-1.1.28/lib --with-exslt-include=/nix/store/j7y29aggnzmlgh5bccp9f7vmiknh16fm-libxslt-1.1.28-dev/include
/nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- ./siteconf20160620-11206-1hntp6t.rb (LoadError)
        from /nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'