Parsing error when variables in dependencies include '='

```make
installed := my_installed=file
built := my_built=file

$(installed): $(built)
cp $< $@
```

This appears to work in make 3.81 & 4.1, but causes a parsing error in kati:

```
Makefile:5: *** commands commence before first target.
```

I believe that it's parsing the '=' sign out of $(built) and setting a target-specific variable instead of using it as a dependency.