a question about one part of gcc manual

[ali hagigat]

3.14 options for directory search
"This is to ensure that GCC's procedure to fix buggy system headers
and the ordering for the include-next directive are not inadvertently
changed.  "

I do not understand this part the gcc manual. What is GCC procedure?
How buggy system headers will be fixed? and what ordering is talking
about? What is include-next the manual is talking about? I wonder if
anybody can study this part and say that in other words.