[xslt] win32 trianon.c defines "const" as empty string

[Tom Moog <tmoog polhode com>]

Compiler MSVC 6 SP5

I'm not sure why, but trianon.c thinks that __STDC__
is undefined.  As a result, it redefines "const"
and "volatile" as empty strings.  Aside from the
fact that this is truly barbaric programming, it
wouldn't cause problems, except that trianon.c
is #included in xpath.c. The result is that all
the const disappear in xpath.c. 

This problem does not appear with gcc 2.95.

trianon.c:82