Document intentional fallthroughs.

Found by: Coverity scan.

grub-core/disk/diskfilter.c

@@ -71,10 +71,12 @@ is_lv_readable (struct grub_diskfilter_lv *lv, int easily)
 	case GRUB_DISKFILTER_RAID6:
 	  if (!easily)
 	    need--;
+	  /* Fallthrough.  */
 	case GRUB_DISKFILTER_RAID4:
 	case GRUB_DISKFILTER_RAID5:
 	  if (!easily)
 	    need--;
+	  /* Fallthrough.  */
 	case GRUB_DISKFILTER_STRIPED:
 	  break;
 
@@ -584,6 +586,7 @@ read_segment (struct grub_diskfilter_segment *seg, grub_disk_addr_t sector,
       if (seg->node_count == 1)
 	return grub_diskfilter_read_node (&seg->nodes[0],
 					  sector, size, buf);
+      /* Fallthrough.  */
     case GRUB_DISKFILTER_MIRROR:
     case GRUB_DISKFILTER_RAID10:
       {

grub-core/font/font.c

@@ -1286,7 +1286,7 @@ blit_comb (const struct grub_unicode_glyph *glyph_id,
 	    - grub_font_get_xheight (combining_glyphs[i]->font) - 1;
 	  if (space <= 0)
 	    space = 1 + (grub_font_get_xheight (main_glyph->font)) / 8;
-
+	  /* Fallthrough.  */
 	case GRUB_UNICODE_STACK_ATTACHED_ABOVE:
 	  do_blit (combining_glyphs[i], targetx,
 		   -(ctx.bounds.height + ctx.bounds.y + space
@@ -1327,6 +1327,7 @@ blit_comb (const struct grub_unicode_glyph *glyph_id,
 		    + combining_glyphs[i]->height);
 	  if (space <= 0)
 	    space = 1 + (grub_font_get_xheight (main_glyph->font)) / 8;
+	  /* Fallthrough.  */
 
 	case GRUB_UNICODE_STACK_ATTACHED_BELOW:
 	  do_blit (combining_glyphs[i], targetx, -(ctx.bounds.y - space),

grub-core/fs/udf.c

@@ -986,6 +986,7 @@ grub_udf_read_symlink (grub_fshelp_node_t node)
 	case 1:
 	  if (ptr[1])
 	    goto fail;
+	  /* Fallthrough.  */
 	case 2:
 	  /* in 4 bytes. out: 1 byte.  */
 	  optr = out;

grub-core/lib/legacy_parse.c

@@ -664,6 +664,7 @@ grub_legacy_parse (const char *buf, char **entryname, char **suffix)
 	  {
 	  case TYPE_FILE_NO_CONSUME:
 	    hold_arg = 1;
+	    /* Fallthrough.  */
 	  case TYPE_PARTITION:
 	  case TYPE_FILE:
 	    args[i] = adjust_file (curarg, curarglen);

grub-core/loader/i386/pc/linux.c

@@ -280,10 +280,13 @@ grub_cmd_linux (grub_command_t cmd __attribute__ ((unused)),
 	      {
 	      case 'g':
 		shift += 10;
+		/* Fallthrough.  */
 	      case 'm':
 		shift += 10;
+		/* Fallthrough.  */
 	      case 'k':
 		shift += 10;
+		/* Fallthrough.  */
 	      default:
 		break;
 	      }

grub-core/normal/charset.c

@@ -929,6 +929,7 @@ grub_bidi_line_logical_to_visual (const grub_uint32_t *logical,
 	  case GRUB_BIDI_TYPE_R:
 	  case GRUB_BIDI_TYPE_AL:
 	    bidi_needed = 1;
+	    /* Fallthrough.  */
 	  default:
 	    {
 	      if (join_state == JOIN_FORCE)

grub-core/video/bochs.c

@@ -359,6 +359,7 @@ grub_video_bochs_setup (unsigned int width, unsigned int height,
     case 32:
       framebuffer.mode_info.reserved_mask_size = 8;
       framebuffer.mode_info.reserved_field_pos = 24;
+      /* Fallthrough.  */
 
     case 24:
       framebuffer.mode_info.red_mask_size = 8;

grub-core/video/cirrus.c

@@ -440,6 +440,7 @@ grub_video_cirrus_setup (unsigned int width, unsigned int height,
     case 32:
       framebuffer.mode_info.reserved_mask_size = 8;
       framebuffer.mode_info.reserved_field_pos = 24;
+      /* Fallthrough.  */
 
     case 24:
       framebuffer.mode_info.red_mask_size = 8;

grub-core/video/i386/pc/vbe.c

@@ -874,6 +874,7 @@ vbe2videoinfo (grub_uint32_t mode,
       /* CGA is basically 4-bit packed pixel.  */
     case GRUB_VBE_MEMORY_MODEL_CGA:
       mode_info->mode_type |= GRUB_VIDEO_MODE_TYPE_CGA;
+      /* Fallthrough.  */
     case GRUB_VBE_MEMORY_MODEL_PACKED_PIXEL:
       mode_info->mode_type |= GRUB_VIDEO_MODE_TYPE_INDEX_COLOR;
       break;
@@ -886,6 +887,7 @@ vbe2videoinfo (grub_uint32_t mode,
       /* Non chain 4 is a special case of planar.  */
     case GRUB_VBE_MEMORY_MODEL_NONCHAIN4_256:
       mode_info->mode_type |= GRUB_VIDEO_MODE_TYPE_NONCHAIN4;
+      /* Fallthrough.  */
     case GRUB_VBE_MEMORY_MODEL_PLANAR:
       mode_info->mode_type |= GRUB_VIDEO_MODE_TYPE_PLANAR
 	| GRUB_VIDEO_MODE_TYPE_INDEX_COLOR;

util/getroot.c

@@ -107,6 +107,7 @@ grub_util_pull_device (const char *os_dev)
     default:
       if (grub_util_pull_device_os (os_dev, ab))
 	return;
+      /* Fallthrough.  */
     case GRUB_DEV_ABSTRACTION_NONE:
       free (grub_util_biosdisk_get_grub_dev (os_dev));
       return;

util/grub-install.c

@@ -1809,7 +1809,7 @@ main (int argc, char *argv[])
 	  grub_install_copy_file (imgfile, dst, 1);
 	  free (dst);
 	}
-
+      /* Fallthrough.  */
     case GRUB_INSTALL_PLATFORM_X86_64_EFI:
       if (efidir_is_mac)
 	{