fix implicit fallthrough gcc warnings

This patch addresses implicit fallthrough warnings on the
newer gcc compiler. Proper comment to silence the warning or appropriate comments
have been added in the case statements.

Signed-off-by: Ani Sinha <ani@anisinha.ca>

Author: ani-sinha

grub-core/commands/hdparm.c

@@ -328,6 +328,7 @@ grub_cmd_hdparm (grub_extcmd_context_t ctxt, int argc, char **args)
 	  ata = ((struct grub_scsi *) disk->data)->data;
 	  break;
 	}
+      // fall through
     default:
       return grub_error (GRUB_ERR_IO, "not an ATA device");
     }

grub-core/disk/cryptodisk.c

@@ -268,6 +268,7 @@ grub_cryptodisk_endecrypt (struct grub_cryptodisk *dev,
 	  break;
 	case GRUB_CRYPTODISK_MODE_IV_PLAIN64:
 	  iv[1] = grub_cpu_to_le32 (sector >> 32);
+	  // fall through
 	case GRUB_CRYPTODISK_MODE_IV_PLAIN:
 	  iv[0] = grub_cpu_to_le32 (sector & 0xFFFFFFFF);
 	  break;

grub-core/disk/diskfilter.c

@@ -71,6 +71,7 @@ is_lv_readable (struct grub_diskfilter_lv *lv, int easily)
 	case GRUB_DISKFILTER_RAID6:
 	  if (!easily)
 	    need--;
+	  // fall through
 	case GRUB_DISKFILTER_RAID4:
 	case GRUB_DISKFILTER_RAID5:
 	  if (!easily)
@@ -507,6 +508,7 @@ 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);
+      // fall through
     case GRUB_DISKFILTER_MIRROR:
     case GRUB_DISKFILTER_RAID10:
       {

grub-core/disk/efi/efidisk.c

@@ -262,6 +262,9 @@ name_devices (struct grub_efidisk_data *devices)
 	    {
 	    case GRUB_EFI_HARD_DRIVE_DEVICE_PATH_SUBTYPE:
 	      is_hard_drive = 1;
+#if defined(__GNUC__) && __GNUC__ >= 7
+	      __attribute__ ((fallthrough));
+#endif
 	      /* Fall through by intention.  */
 	    case GRUB_EFI_CDROM_DEVICE_PATH_SUBTYPE:
 	      {

grub-core/efiemu/mm.c

@@ -410,6 +410,7 @@ grub_efiemu_mmap_fill (void)
 	default:
 	  grub_dprintf ("efiemu",
 			"Unknown memory type %d. Assuming unusable\n", type);
+	  // fall through
 	case GRUB_MEMORY_RESERVED:
 	  return grub_efiemu_add_to_mmap (addr, size,
 					  GRUB_EFI_UNUSABLE_MEMORY);

grub-core/font/font.c

@@ -1297,6 +1297,7 @@ 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;
+	  // fall through
 
 	case GRUB_UNICODE_STACK_ATTACHED_ABOVE:
 	  do_blit (combining_glyphs[i], targetx,
@@ -1338,6 +1339,7 @@ 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;
+	  // fall through
 
 	case GRUB_UNICODE_STACK_ATTACHED_BELOW:
 	  do_blit (combining_glyphs[i], targetx, -(bounds.y - space));

grub-core/fs/udf.c

@@ -970,6 +970,7 @@ grub_udf_read_symlink (grub_fshelp_node_t node)
 	case 1:
 	  if (ptr[1])
 	    goto fail;
+	  // fall through
 	case 2:
 	  /* in 4 bytes. out: 1 byte.  */
 	  optr = out;

grub-core/gdb/cstub.c

@@ -336,6 +336,7 @@ grub_gdb_trap (int trap_no)
 	/* sAA..AA: Step one instruction from AA..AA(optional).  */
 	case 's':
 	  stepping = 1;
+	  // fall through
 
 	/* cAA..AA: Continue at address AA..AA(optional).  */
 	case 'c':

grub-core/gnulib/regexec.c

@@ -4104,8 +4104,8 @@ check_node_accept (const re_match_context_t *mctx, const re_token_t *node,
     case OP_UTF8_PERIOD:
       if (ch >= ASCII_CHARS)
         return false;
-      /* FALLTHROUGH */
 #endif
+      // fall through
     case OP_PERIOD:
       if ((ch == '\n' && !(mctx->dfa->syntax & RE_DOT_NEWLINE))
 	  || (ch == '\0' && (mctx->dfa->syntax & RE_DOT_NOT_NULL)))

grub-core/lib/legacy_parse.c

@@ -626,6 +626,7 @@ grub_legacy_parse (const char *buf, char **entryname, char **suffix)
 	  {
 	  case TYPE_FILE_NO_CONSUME:
 	    hold_arg = 1;
+	    // fall through
 	  case TYPE_PARTITION:
 	  case TYPE_FILE:
 	    args[i] = adjust_file (curarg, curarglen);