NO-OP: fix some Wimplicit-fallthrough

gcc can recognize various regexps in comments. Since C++17 provides
[[fallthrough]], using /* fallthrough */ consistently seems
appropriate until we switch to C++17.

see also https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

tools/luadevel/devel.cc

@@ -155,10 +155,11 @@ class LuaTableRef {
 							// invalid userdata -- fall through
 						}
 
-						/* fall through */
+						/* fallthrough */
 					case LUA_TFUNCTION: // no support -- we could... string.format("%q", string.dump(value, true))
 					case LUA_TTABLE: // no nested tables, sorry.
-					case LUA_TNIL: // fallthrough
+					case LUA_TNIL:
+						/* fallthrough */
 					default:
 						// invalid value
 						lua_pop (L, 2);