Convert most remaining free-form fall-through comments to FALLTHROUGH

One exception is src/amd/addrlib/, for which -Wimplicit-fallthrough is
explicitly disabled.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10220>

src/intel/compiler/brw_fs_builder.h

@@ -822,7 +822,7 @@ namespace brw {
                 src.width != BRW_WIDTH_8 ||
                 src.hstride != BRW_HORIZONTAL_STRIDE_1)
                break;
-            /* fallthrough */
+            FALLTHROUGH;
          case ATTR:
          case VGRF:
          case UNIFORM: