lib/ww/lex: port the u64 overflow guard into parseint (#53)

wwstage parseint dropped the pre-multiply overflow guard the C twin
carries (cmd/wcc/lex.c:156, if (v > (u64)~0ULL / (u64)base)), so any
integer literal exceeding u64 was silently accepted mod 2^64 while
cstage loudly rejected with 'bad integer literal' — a rule-10 stage
divergence and a silent wrong constant. Port the guard before the
multiply-add; wwstage now rejects in lockstep with cstage.

lib/ww embeds into the w6c/wwdump combined.ww snapshots; both regen'd.
989_intoverflow_reject pins the reject-matrix on both driver twins.

Makefile

@@ -249,6 +249,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_tagged_subset_reject \
 	  $(BIN)/test_callarg_typecheck \
 	  $(BIN)/test_catA_f2_reject \
+	  $(BIN)/test_intoverflow_reject \
 	  $(BIN)/test_idxarg_run \
 	  $(BIN)/test_chainidx_run \
 	  $(BIN)/test_tupfieldsize_run \
@@ -685,6 +686,17 @@ $(BIN)/test_catA_f2_reject: test/wcc/989_catA_f2_reject.c \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+# 989_intoverflow_reject (F14 #53): an integer literal that overflows u64
+# must FAIL to build on BOTH driver twins (wwstage parseint dropped the C
+# twin's overflow guard). Needs the full cstage + wwstage tool sets plus
+# libwwrt for the control links.
+$(BIN)/test_intoverflow_reject: test/wcc/989_intoverflow_reject.c \
+		$(BIN)/ww $(BIN)/ww_ww \
+		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 # 989_idxarg_run (F7-c2, #45/#46): an indexed slice/str element passed as
 # a call arg must push its full multi-word header. Builds+runs each fixture
 # on BOTH the cstage `ww` and wwstage `ww_ww` drivers (rule-10), so it needs