llvmpipe: Disable multithreading on windows.

src/gallium/drivers/llvmpipe/lp_rast.c

@@ -939,9 +939,15 @@ create_rast_threads(struct lp_rasterizer *rast)
 {
    unsigned i;
 
+#ifdef PIPE_OS_WINDOWS
+   /* Multithreading not supported on windows until conditions and barriers are
+    * properly implemented. */
+   rast->num_threads = 0;
+#else
    rast->num_threads = util_cpu_caps.nr_cpus;
    rast->num_threads = debug_get_num_option("LP_NUM_THREADS", rast->num_threads);
    rast->num_threads = MIN2(rast->num_threads, MAX_THREADS);
+#endif
 
    /* NOTE: if num_threads is zero, we won't use any threads */
    for (i = 0; i < rast->num_threads; i++) {