the gcc "private" include dir

["John Lumby" <johnlumby@xxxxxxxxxxx>]

Excuse my terminology if it's incorrect.    I'd like to understand what 
controls/tells a particular gcc executable whether to search its "private" 
include dir and if so where that is.      What I mean by "private include 
dir" is a directory named "include" that appears to be solely for, and 
installed as part of, gcc, and is also gcc-release specific.    For example, 
it contains header files such as "stdarg.h" which (at least on my system) 
are not found anywhere else.   (This file, amongst other things, defines the 
typedef "va_list" to be a compiler built-in)

On my RedHat system, which came with gcc-2.96 and on which I've subsequently 
installed newer gcc's such as 3.3.3 and 3.4.0, I see these private include 
dirs:

/usr/lib/gcc-lib/i386-redhat-linux/2.96/include
/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3/include
/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/include
/usr/local/lib/gcc-lib/glibc2/3.3/include
/usr/local/lib/gcc-lib/glibc2/3.3.1/include
/usr/local/lib/gcc/i686-pc-linux-gnu/3.4.0/include

After the most recentl install, of 3.4.0, which works perfectly, I needed to 
run the original 2.96 compiler.   I still had the 2.96 gcc executable and it 
ran ok but the compilation failed with
  include/linux/kernel.h:10:20: stdarg.h: No such file or directory
It appears as though the 2.96 gcc has "forgotten" where its private include 
dir is.   When compiling the same file with 3.4.0, it finds its stdarg.h, 
but  I need it compiled with 2.96.

Can anyone explain how this all works and what is the correct procedure for 
switching from one release to another previously installed one.

John

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