glsl: Add a file argument to the IR printer.

While we want to be able to print to stdout for glsl_compiler, for
debugging drivers we want to be able to dump to stderr because that's
where other driver debug (like LIBGL_DEBUG) tends to go, and because some
apps actually close stdout to shut up their own messages (such as the X
Server, or NWN).

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/glsl/opt_array_splitting.cpp

@@ -400,7 +400,7 @@ optimize_split_arrays(exec_list *instructions, bool linked)
    visit_list_elements(&split, instructions);
 
    if (debug)
-      _mesa_print_ir(instructions, NULL);
+      _mesa_print_ir(stdout, instructions, NULL);
 
    ralloc_free(mem_ctx);