src/c-types-parse.lisp: Use the new `find-simple-c-type' function.

src/c-types-parse.lisp: Use the new `find-simple-c-type' function.

New simple types added using `define-simple-c-type' won't be present in
the `*declspec-map*', or the `*module-type-map*', so they won't be found
at all using the previous search.  Now, look use `find-simple-c-type' if
the other two lookups don't work.

Now that this works, we don't need `void' or `bool' in the `*declspec-
map*', because they don't accept any modifiers.