intel/fs: add variable for output of debug backend optimizer

It can be useful to compare 2 runs with different compiler changes.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24552>

src/intel/compiler/brw_fs.cpp

@@ -6200,7 +6200,8 @@ fs_visitor::debug_optimizer(const char *pass_name,
       return;
 
    char *filename;
-   int ret = asprintf(&filename, "%s%d-%s-%02d-%02d-%s",
+   int ret = asprintf(&filename, "%s/%s%d-%s-%02d-%02d-%s",
+                      debug_get_option("INTEL_SHADER_OPTIMIZER_PATH", "./"),
                       stage_abbrev, dispatch_width, nir->info.name,
                       iteration, pass_num, pass_name);
    if (ret == -1)