Gem intallation fails on "checking for xmlParseDoc() in -lxml2... no" With 64-bit libxml2 DLLs included with Gem (Windows)

[SimonKaluza]

If I use the new 64-bit libxml2-2.dll included at https://github.com/xml4r/libxml-ruby/tree/v2.9.0/lib/libs the compilation step of the native bindings fails during gem installations on Ruby 2.1.x with:

gem install libxml-ruby --platform=x64-mingw32
Building native extensions.  This could take a while...
ERROR:  Error installing libxml-ruby:
        ERROR: Failed to build gem native extension.

    D:/Ruby21-x64/bin/ruby.exe extconf.rb
checking for libxml/xmlversion.h in /opt/include/libxml2,/opt/local/include/libxml2,/usr/local/include/libxml2,/usr/include/libxml2... yes
checking for xmlParseDoc() in -lxml2... no
*** extconf.rb failed ***

Oddly enough, if I replace the libxml2 DLL with the one contained in this distribution https://forge.imag.fr/frs/?group_id=184&release_id=320 the gem compiles and installs successfully but it then fails at run-time with:

irb(main):001:0> require 'libxml'
LoadError: 126: The specified module could not be found.   - D:/Ruby21-x64/lib/ruby/gems/2.1.0/extensions/x64-mingw32/2.1.0/libxml-ruby-2.9.0/libxml_ruby.so
        from D:/Ruby21-x64/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
        from D:/Ruby21-x64/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
        from D:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/libxml-ruby-2.9.0/lib/libxml.rb:8:in `rescue in <top (required)>'
        from D:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/libxml-ruby-2.9.0/lib/libxml.rb:4:in `<top (required)>'
        from D:/Ruby21-x64/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:135:in `require'
        from D:/Ruby21-x64/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:135:in `rescue in require'
        from D:/Ruby21-x64/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:144:in `require'
        from (irb):1
        from D:/Ruby21-x64/bin/irb:11:in `<main>'
irb(main):002:0>

This is even stranger because I've manually verified that the file libxml_ruby.so exists and is correctly installed at the location D:/Ruby21-x64/lib/ruby/gems/2.1.0/extensions/x64-mingw32/2.1.0/libxml-ruby-2.9.0/libxml_ruby.so, the error message identified above.

Note that I've also tried copying the libxml2.dll (both from the latter and former distribution to various other locations on the run-time path as described by #91 (comment) did not resolve it for me. The other solutions available at http://stackoverflow.com/questions/22417544/having-trouble-installing-libxml-ruby-on-windows/33685307#33685307 did not resolve it either.

Does anybody have any suggestions for how to get this working and/or debug this issue on Windows?

[cfis]

If you install the binary version of the gem, then no compiling should be happening at all. So that doesn't make a lot of sense.

Try putting the so file in gems/2.1.0/gems/libxml-ruby-2.9.0/lib

[cfis]

Going to close - reopen if you still need help.