gallium/ddebug: add GALLIUM_DDEBUG_SKIP option

When we know that hangs occur only very late in a reproducible run (e.g.
apitrace), we can save a lot of debugging time by skipping the flush and hang
detection for earlier draw calls.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/drivers/ddebug/dd_screen.c

@@ -290,6 +290,9 @@ ddebug_screen_create(struct pipe_screen *screen)
       puts("    $HOME/"DD_DIR"/ when a hang is detected.");
       puts("    If 'noflush' is specified, only detect hangs in pipe->flush.");
       puts("");
+      puts("  GALLIUM_DDEBUG_SKIP=[count]");
+      puts("    Skip flush and hang detection for the given initial number of draw calls.");
+      puts("");
       exit(0);
    }
 
@@ -349,5 +352,11 @@ ddebug_screen_create(struct pipe_screen *screen)
       assert(0);
    }
 
+   dscreen->skip_count = debug_get_num_option("GALLIUM_DDEBUG_SKIP", 0);
+   if (dscreen->skip_count > 0) {
+      fprintf(stderr, "Gallium debugger skipping the first %u draw calls.\n",
+              dscreen->skip_count);
+   }
+
    return &dscreen->base;
 }