Error on unfulfilled cond-expand.

This complies with the SRFI 0 specification, and avoids the undefined
behavior of R7RS.

lib/chibi/emscripten.stub

@@ -4,4 +4,5 @@
 
     (define-c void (eval-script! "emscripten_run_script") (string))
     (define-c int (integer-eval-script "emscripten_run_script_int") (string))
-    (define-c string (string-eval-script "emscripten_run_script_string") (string))))
+    (define-c string (string-eval-script "emscripten_run_script_string") (string)))
+  (else))

lib/init-7.scm

@@ -382,7 +382,7 @@
            (memq (identifier->symbol x) *features*)))
      (let expand ((ls (cdr expr)))
        (cond
-        ((null? ls))  ; (error "cond-expand: no expansions" expr)
+        ((null? ls) (error "cond-expand: no expansions" expr))
         ((not (pair? (car ls))) (error "cond-expand: bad clause" (car ls)))
         ((eq? 'else (identifier->symbol (caar ls)))
          (if (pair? (cdr ls))

lib/srfi/144/math.stub

@@ -171,7 +171,8 @@ double sexp_compute_least_double(double f) {
 (define-c double (flgamma "tgamma") (double))
 (cond-expand
   (windows
-   (c-include-verbatim "lgamma_r.c")))
+   (c-include-verbatim "lgamma_r.c"))
+  (else))
 (define-c double lgamma_r (double (result int)))
 
 (define-c double (flfirst-bessel "jn") (int double))