libsepol,libsemanage,libselinux: Fix fallthrough warnings from gcc 7

https://developers.redhat.com/blog/2017/03/10/wimplicit-fallthrough-in-gcc-7/

Fixes the following warnings by annotating with a /* FALLTHRU */ comment.
Unfortunately, the __attribute__ ((fallthrough)); approach does not appear
to work with older compilers.

../cil/src/cil_parser.c: In function ‘cil_parser’:
../cil/src/cil_parser.c:253:14: warning: this statement may fall through [-Wimplicit-fallthrough=]
    tok.value = tok.value+1;
    ~~~~~~~~~~^~~~~~~~~~~~~
../cil/src/cil_parser.c:254:3: note: here
   case SYMBOL:
   ^~~~
../cil/src/cil_parser.c:275:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    if (tok.type != END_OF_FILE) {
       ^
../cil/src/cil_parser.c:279:3: note: here
   case END_OF_FILE:
   ^~~~

../cil/src/cil_post.c: In function ‘cil_post_fc_fill_data’:
../cil/src/cil_post.c:104:5: warning: this statement may fall through [-Wimplicit-fallthrough=]
    c++;
    ~^~
../cil/src/cil_post.c:105:3: note: here
   default:
   ^~~~~~~

regex.c: In function ‘regex_format_error’:
regex.c:541:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
   *ptr++ = '.';
   ~~~~~~~^~~~~
regex.c:542:2: note: here
  case 3:
  ^~~~
regex.c:543:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
   *ptr++ = '.';
   ~~~~~~~^~~~~
regex.c:544:2: note: here
  case 2:
  ^~~~
regex.c:545:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
   *ptr++ = '.';
   ~~~~~~~^~~~~
regex.c:546:2: note: here
  case 1:
  ^~~~
regex.c: In function ‘regex_format_error’:
regex.c:541:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
   *ptr++ = '.';
   ~~~~~~~^~~~~
regex.c:542:2: note: here
  case 3:
  ^~~~
regex.c:543:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
   *ptr++ = '.';
   ~~~~~~~^~~~~
regex.c:544:2: note: here
  case 2:
  ^~~~
regex.c:545:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
   *ptr++ = '.';
   ~~~~~~~^~~~~
regex.c:546:2: note: here
  case 1:
  ^~~~

modules.c: In function ‘semanage_module_get_path’:
modules.c:602:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    if (file == NULL) file = "hll";
       ^
modules.c:603:3: note: here
   case SEMANAGE_MODULE_PATH_CIL:
   ^~~~
modules.c:604:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    if (file == NULL) file = "cil";
       ^
modules.c:605:3: note: here
   case SEMANAGE_MODULE_PATH_LANG_EXT:
   ^~~~

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

libselinux/src/regex.c

@@ -539,12 +539,16 @@ truncated:
 	/* no break statements, fall-through is intended */
 	case 4:
 		*ptr++ = '.';
+		/* FALLTHRU */
 	case 3:
 		*ptr++ = '.';
+		/* FALLTHRU */
 	case 2:
 		*ptr++ = '.';
+		/* FALLTHRU */
 	case 1:
 		*ptr++ = '\0';
+		/* FALLTHRU */
 	default:
 		break;
 	}

libsemanage/src/modules.c

@@ -600,8 +600,10 @@ int semanage_module_get_path(semanage_handle_t *sh,
 			break;
 		case SEMANAGE_MODULE_PATH_HLL:
 			if (file == NULL) file = "hll";
+			/* FALLTHRU */
 		case SEMANAGE_MODULE_PATH_CIL:
 			if (file == NULL) file = "cil";
+			/* FALLTHRU */
 		case SEMANAGE_MODULE_PATH_LANG_EXT:
 			if (file == NULL) file = "lang_ext";
 

libsepol/cil/src/cil_parser.c

@@ -251,6 +251,7 @@ int cil_parser(char *_path, char *buffer, uint32_t size, struct cil_tree **parse
 		case QSTRING:
 			tok.value[strlen(tok.value) - 1] = '\0';
 			tok.value = tok.value+1;
+			/* FALLTHRU */
 		case SYMBOL:
 			if (paren_count == 0) {
 				cil_log(CIL_ERR, "Symbol not inside parenthesis at line %d of %s\n", tok.line, path);
@@ -275,6 +276,7 @@ int cil_parser(char *_path, char *buffer, uint32_t size, struct cil_tree **parse
 			if (tok.type != END_OF_FILE) {
 				break;
 			}
+			/* FALLTHRU */
 			// Fall through if EOF
 		case END_OF_FILE:
 			if (paren_count > 0) {

libsepol/cil/src/cil_post.c

@@ -102,6 +102,7 @@ void cil_post_fc_fill_data(struct fc_data *fc, char *path)
 			break;
 		case '\\':
 			c++;
+			/* FALLTHRU */
 		default:
 			if (!fc->meta) {
 				fc->stem_len++;