Is there any guru know sth about " #include_next "?

We are running SUNOS 4.1.3 and the g++-include files are
installed at /usr/local/lib/gcc/g++-include/.
One of the header file, stdio.h, contains the following
line:  #include_next <stdio.h>

And after we try g++ the program which include this stdio.h,
we get

0: unknown flag -lang-c++
/usr/local/gcc/lib/g++-include/stdio.h: 25: undefined control

#include_next just lies in that line!

Any help will be greatly appreciated!
Please reply to MY EMAIL ADDRESS, 'cause I can't read news.
Thanks a lot in advance!