give fmt-c a name for every parameter

fmt-c takes a parameter's name with `cadr', so an unnamed one handed
over bare lost its second word to it: `(* const char)' dropped its
star, and `(int)' had no second word at all.

Makefile

@@ -98,7 +98,7 @@ sextest:
 
 SEX_TEST_PROGRAMS = hello-world lists comments unicode serialize features \
                     feature-flags lambdas compound-literals closures fixpoint \
-                    wildcards inference type-shapes
+                    wildcards inference type-shapes unnamed-params
 
 # Multi-module linking is checked end to end; see tests/modules/Makefile.
 check-modules: sexc