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/amd/vulkan/radv_nir_to_llvm.c

@@ -1084,7 +1084,7 @@ radv_emit_stream_output(struct radv_shader_context *ctx, LLVMValueRef const *so_
    case 2: /* as v2i32 */
    case 3: /* as v4i32 (aligned to 4) */
       out[3] = LLVMGetUndef(ctx->ac.i32);
-      /* fall through */
+      FALLTHROUGH;
    case 4: /* as v4i32 */
       vdata = ac_build_gather_values(&ctx->ac, out,
                                      !ac_has_vec3_support(ctx->ac.chip_class, false)