Please take a look at the config.log, and locate the lines

In file included from
/usr/GNU/lib/gcc-lib/sparc-sun-solaris2.4/2.6.3/include/time.h:90,
                 from /usr/include/sys/time.h:418,
                 from /usr/include/sys/termios.h:23,
                 from /usr/include/sys/termio.h:13,
                 from /usr/include/termio.h:13,
                 from
/usr/GNU/lib/gcc-lib/sparc-sun-solaris2.4/2.6.3/include/curses.h:48,
                 from conftest.c:47:
/usr/include/sys/siginfo.h:74: parse error before `pthread_attr_t'

Then please take a look at line 90 of
/usr/GNU/lib/gcc-lib/sparc-sun-solaris2.4/2.6.3/include/time.h
and confirm that it indeed includes siginfo.h at that line.

Then please compare /usr/include/time.h with
/usr/GNU/lib/gcc-lib/sparc-sun-solaris2.4/2.6.3/include/time.h
and report any differences that you see.

To me, it seems that your compiler's header files don't match your
system's header files. This is not surprising, as gcc 2.6.3 was released
in 1994, years before Solaris 9 was released; your gcc was build for
Solaris 2.4. You probably need to run fixincludes again (i.e. rebuild
gcc for your system), or install a newer version of gcc entirely.