If you get errors like these:

In file included from /usr/include/sys/signal.h:34,
from /usr/include/signal.h:26,
...
/usr/include/sys/siginfo.h:259: error: parse error before "ctid_t"

And if you use GCC 3.3.2 from sunfreeware.com, then try this:
cd /usr/local/lib/gcc-lib/sparc-sun-solaris2.10/3.3.2/install-tools
./mkheaders