Fix load_varargs to prevent local var corruption

Assigning to a varargs variable that is not passed by the C caller can result in corruption of another parameter. EG: the var contains data for another parameter, which is then changed unexpectedly. The code was rewritten to assign to a new variable, to prevent this from happening.

cgen.scm

@@ -878,7 +878,7 @@
          ((pair? (cdr formals))
           (string-append ", " (c-compile-formals (cdr formals) type)))
          ((not (equal? 'args:fixed type)) 
-          (string-append ", object " (mangle (cdr formals)) ", ..."))
+          (string-append ", object " (mangle (cdr formals)) "_raw, ..."))
          (else
           "")))))
 
@@ -925,7 +925,9 @@
                            ;  (number->string (length (lambda-formals->list exp))) ");"
                            "load_varargs(" 
                            (mangle (lambda-varargs-var exp))
-                           ", argc - " (number->string 
+                           ", "
+                           (mangle (lambda-varargs-var exp))
+                           "_raw, argc - " (number->string 
                                          (- (length (lambda-formals->list exp)) 
                                             1
                                             (if has-closure? 1 0)))

runtime.h

@@ -37,28 +37,27 @@ static object cell_get(object cell){
    our compiler will compute the difference between the number of required
    args and the number of provided ones, and pass the difference as 'count'
  */
-#define load_varargs(var, count) { \
-  int i; \
-  object tmp; \
-  list args = nil; \
-  va_list va; \
-  if (count > 0) { \
-    args = alloca(sizeof(cons_type)*count); \
-    va_start(va, var); \
-    for (i = 0; i < count; i++) { \
-      if (i) { \
-          tmp = va_arg(va, object); \
-      } else { \
-          tmp = var; \
+#define load_varargs(var, arg_var, count) \
+  list var = (count > 0) ? alloca(sizeof(cons_type)*count) : nil; \
+  { \
+    int i; \
+    object tmp; \
+    va_list va; \
+    if (count > 0) { \
+      va_start(va, arg_var); \
+      for (i = 0; i < count; i++) { \
+        if (i) { \
+            tmp = va_arg(va, object); \
+        } else { \
+            tmp = arg_var; \
+        } \
+        var[i].tag = cons_tag; \
+        var[i].cons_car = tmp; \
+        var[i].cons_cdr = (i == (count-1)) ? nil : &var[i + 1]; \
       } \
-      args[i].tag = cons_tag; \
-      args[i].cons_car = tmp; \
-      args[i].cons_cdr = (i == (count-1)) ? nil : &args[i + 1]; \
+      va_end(va); \
     } \
-    va_end(va); \
-  } \
-  var = args; \
-}
+  }
 
 /* Prototypes for Lisp built-in functions. */