wcc: tuple-param ABI via SSE/GP arg cursors (#163)

Tuples were unhandled as parameters — no tuple arm in arg-push, arg-pop, or
callee-recv in either stage — so a tuple param fell to the 1-GP-word else and
dropped all but its first element (integer tuple params too; floats doubly
lost). Add tuple-param arms (SEND push+pop, callee RECV) across both stages,
reusing #164's per-element SysV classify with the 6-GP (DI,SI,DX,CX,R8,R9) +
8-SSE (X0-X7) arg cursors. A frame slot @tupargscr decouples the producing
call's return cursor from the overlapping arg cursor (capture-before-clobber).
Overflow (>6 GP / >8 SSE) fails loud (rule 7). Scoped to the N_CALL producer;
first-class tuple values (ident/literal) remain a separate unimplemented gap.

Gate-blind (the bootstrap passes no tuple params) — covered by table-driven
probe 905, which proves pre-fix element-drop and the loud-stop.

Makefile

@@ -353,6 +353,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_f32stamp_run \
 	  $(BIN)/test_f32arg_run \
 	  $(BIN)/test_tuprecv_f64_run \
+	  $(BIN)/test_tupparam_run \
 	  $(BIN)/test_floats_run \
 	  $(BIN)/test_size_type_run \
 	  $(BIN)/test_types_sizelim_run \
@@ -1266,6 +1267,11 @@ $(BIN)/test_tuprecv_f64_run: test/wcc/956_tuprecv_f64_run.c $(BIN)/ww \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_tupparam_run: test/wcc/905_tupparam_run.c $(BIN)/ww \
+		$(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 sizelint:
 	@sh tools/sizelint