c++/7327: -isystem and template linkage

[Ben Hines]

This bug# 7327 also affects Apple's GCC on Mac OS X. Also, "idirafter" 
is also affected in addition to "isystem".

To reproduce on mac os x:

in conftest.cpp:

#include <conftest.h>
int main ()
{
   return 0;
}

in conftest.h in pwd:
#include <iosfwd>

Compile with:

g++ -idirafter `pwd` conftest.cpp -save-temps
OR
g++ -isystem `pwd` conftest.cpp -save-temps

RESULT:
  % g++ -idirafter `pwd` conftest.cpp -save-temps
In file included from /usr/include/gcc/darwin/3.1/g++-v3/iosfwd:45,
                  from /Users/ben/tempbug/conftest.h:1,
                  from conftest.cpp:2:
/usr/include/gcc/darwin/3.1/g++-v3/bits/stringfwd.h:49: template with C 
linkage
/usr/include/gcc/darwin/3.1/g++-v3/bits/stringfwd.h:57: template with C 
linkage
/usr/include/gcc/darwin/3.1/g++-v3/bits/stringfwd.h:61: template with C 
linkage
-snip more-

REGRESSION:
If i include <iosfwd> directly in conftest.cpp, i don't get the 
problem. It has to be in a header found by isystem.

% gcc -v
Reading specs from /usr/libexec/gcc/darwin/ppc/3.1/specs
Thread model: posix
Apple Computer, Inc. GCC version 1161, based on gcc version 3.1 
20020420 (prerelease)

% uname -a
Darwin lsanca1-ar8-4-60-073-020.lsanca1.dsl-verizon.net 6.1 Darwin 
Kernel Version 6.1: Fri Sep  6 23:24:34 PDT 2002;
root:xnu/xnu-344.2.obj~2/RELEASE_PPC  Power Macintosh powerpc

-Ben