Filter: Ensure that all expressions declared return type

All instructions with a return value (i.e. expressions, ones with
non-zero outval, third argument in INST()) should declare their return
type. Check that automatically by M4 macros.

Set outval of FI_RETURN to 0. The instruction adds one value to stack,
but syntactically it is a statement, not an expression.

Add fake return type declaration to FI_CALL, otherwise the automatic
check would fail builds.

filter/f-inst.c

@@ -1103,7 +1103,7 @@
     }
   }
 
-  INST(FI_RETURN, 1, 1) {
+  INST(FI_RETURN, 1, 0) {
     NEVER_CONSTANT;
     /* Acquire the return value */
     ARG_ANY(1);
@@ -1134,6 +1134,9 @@
     VARARG;
     SYMBOL;
 
+    /* Fake result type declaration */
+    RESULT_TYPE(T_VOID);
+
     FID_NEW_BODY()
     ASSERT(sym->class == SYM_FUNCTION);
 
@@ -1443,7 +1446,7 @@
 
   }
 
-  INST(FI_FORMAT, 1, 0) {	/* Format */
+  INST(FI_FORMAT, 1, 1) {	/* Format */
     ARG_ANY(1);
     RESULT(T_STRING, s, val_format_str(fpool, &v1));
   }