On Debian, the arch specific headear files are available in:
/usr/include/x86_64-linux-gnu/ruby-2.1.0
while the current code is looking for:
/usr/include/ruby-2.1.0/x86_64-linux-gnu
This prevents the compiler to find ruby/config.h.
Since Ruby 2.0, RbConfig::CONFIG['rubyarchhdrdir'] contains the proper
arch header directory, so use it in priority when available.
On Debian, the arch specific headear files are available in: /usr/include/x86_64-linux-gnu/ruby-2.1.0 while the current code is looking for: /usr/include/ruby-2.1.0/x86_64-linux-gnu This prevents the compiler to find ruby/config.h.
Since Ruby 2.0, RbConfig::CONFIG['rubyarchhdrdir'] contains the proper arch header directory, so use it in priority when available.