libstdc++ headers and system headers

[Richard Kenner]

    I can't see anything in the definition of -I which would suggest that
    it could not be used for system header directories.

Well, the existance of -isystems sort of implies it, but I just made it
clearer:

Sun Feb 18 09:30:09 2001  Richard Kenner  <kenner@vlsi1.ultra.nyu.edu>

	* invoke.texi (-I): Add note avoiding use for system header files.

*** invoke.texi	2001/02/17 23:45:54	1.278
--- invoke.texi	2001/02/18 14:44:11
***************
*** 3793,3798 ****
  searched for header files.  This can be used to override a system header
  file, substituting your own version, since these directories are
! searched before the system header file directories.  If you use more
! than one @samp{-I} option, the directories are scanned in left-to-right
  order; the standard system directories come after.
  
--- 3794,3801 ----
  searched for header files.  This can be used to override a system header
  file, substituting your own version, since these directories are
! searched before the system header file directories.  However, you should
! not use this option to add directories that contain vendor-supplied
! system header files (use @samp{-isystem} for that). If you use more than
! one @samp{-I} option, the directories are scanned in left-to-right
  order; the standard system directories come after.