compile lvm.c as cpp code fails at 'goto condjump'

[zerofighter <zerofighter@...>]

for some reason, I'm compiling lua as a single cpp code (unity builds), that is, supply a `cpp` file that include all `*.c` files of lua source code

everything's fine until the recently lua 5.3.4, the `goto condjump` (e.g. lvm.c at line 1475) cause these issue

```

lvm.c:1475:9: error: cannot jump from this goto statement to its label

    goto condjump;

lvm.c:1402:17: note: jump bypasses variable initialization

    TValue *rb = vRB(i);

```

would you please to support cpp unity builds compile method? Thanks