The Foreign Parser automates the generation of Foreign Language Interface defining forms, given files containing C declarations.
The result does often need some editing, due to ambiguities in C.
The Foreign Parser requires a C preprocessor, so you must have a suitable preprocessor installed on your machine.
By default LispWorks invokes cl.exe (VC++) on Windows and cc on other platforms. If you have this installed, then make sure it is on your PATH.
On Windows, if you don't have cl.exe, download the VC++ toolkit from Microsoft.
Preprocessors known to work with LispWorks are:
To use a preprocessor other than the default, set the variable foreign-parser:*preprocessor*, for example:
(setf foreign-parser:*preprocessor* "gcc")
LispWorks Foreign Language Interface User Guide and Reference Manual - 29 Sep 2017