luajit adds source to kwargs breaking linking with Rust

The LuaJIT wrap adds the `luajit_h` target as a source, thus adding the file `luajit.h` when specifying luajit as a dependency. This is usually not a problem for C/C++, but when linking to Rust, this will cause the compilation to fail with "ERROR: Rust target FOO contains a non-rust source file.". The [offending code](https://github.com/mesonbuild/wrapdb/blob/master/subprojects/packagefiles/luajit/src/meson.build#L169) is:
```python
luajit_dep_kwargs = {
'include_directories': include_directories('.'),
'sources' : luajit_h,
'variables' : {
'INSTALL_CMOD' : install_cmod,
'INSTALL_LMOD' : install_lmod,
},
}
```
My code only hits the issue with the fallback, it works fine with the system library.

Open subprojects/packagefiles/luajit/src/meson.build around line 169 and inspect how luajit_dep_kwargs is assembled. Reproduce the fallback dependency with a Rust target, then verify that the dependency no longer contributes luajit.h as a source and the Rust target can compile.

Written by the indexing model from the issue text.