When installing an extension library which provides a header, that header should be installed under site_ruby (or vendor_ruby when "--vendor" option was given to extconf.rb).
However, currently this file is about to be installed in the core include directory.
mkmf: fixed install directories of header files in extension libraries [Bug #17761]
When installing an extension library which provides a header, that
header should be installed under site_ruby (or vendor_ruby when
"--vendor" option was given to extconf.rb). However, currently
this file is about to be installed in the core include directory.