Dejagnu: use -isystem to include system header files.

[Nick Clifton]

Hi Richard,

> The issue wasn't really about picking up gcc/include/limits.h over
> newlib/include/limits.h, it was about how we processed the newlib
> version when in strict ANSI mode.  That should be handled correctly when
> we use -isystem (because that relaxes the rules).  So I think we should
> try and get the search order back to what it was before, but when still
> using -isystem.

I am not sure that this is possible.  The <build-dir>/gcc/include 
directory is added via an -isystem switch that is synthesised by the gcc 
(or xgcc) compiler driver.  It is processed before any-isystem switch 
specified by the user on the command line so that gcc's fixed versions 
of system header files will be included before the systems.  Thus if the 
dejagnu test harness uses the -isystem switch to add the 
newlib/libc/include directory it is always going to be after 
<build-dir>/gcc/include in the list of directories searched.

This sounds correct to me.  The intention is that the fixed version of 
limits.h should be included before the system version of limits.h.  Thus 
builtins-config.h should not assume that #include <limits.h> will return 
the system limits.h.  It might well return a fixed version instead.

Cheers
   Nick