wcc/check: #141 def-dim array as struct field — fold def in dim, shared arrayelen across 3 ww readers (both stages)

A def-dimensioned array [MAX]u8 used as a struct field was BOTH-WRONG: cstage
loud-rejected ("array length must be an integer literal"); wwstage silently
sized the dim to 0, so the next field overlapped it (frame-smash). The
reference is neither stage — it is Hare: accept + fold the def.

cstage: fold the def into the dim via eval_def_const. The fold needs def NAMES
visible when resolve_typedecl walks struct bodies, so a stub loop binds
def-name stubs (type=NULL, filled in place by the existing def loop) before
resolve_typedecl — this extends check_file's existing names-first USE+TYPEDECL
pass to DEFs; def-TYPE resolution stays in its original order, and the
kind-filtered type lookup (#225) keeps the SK_DEF stub out of type position.

wwstage: one shared arrayelen(c, rhs) (INTLIT -> uval; else evaldefconst;
else 0) routed through astsize / tinfofornode / checkarrlitfits.

Closes #13's def-dim cstage-reject half (the slice-repeat clause stays open).
Pin test/wcc/951 (5 rows incl a cross-module os.PATH_MAX dim + a ~4KB shape;
teeth = cstage loud-reject + ww frame-smash). cgen-first blocker for the
path::buffer arc (type buffer = struct{[MAX]u8, ...}).

Makefile

@@ -467,6 +467,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_dotbase_arr_run \
 	  $(BIN)/test_dotbase_addr_slice_run \
 	  $(BIN)/test_structlit_arrfield_run \
+	  $(BIN)/test_defdim_struct_run \
 	  $(BIN)/test_arraytoslice_run \
 	  $(BIN)/test_arrlit_slice_run \
 	  $(BIN)/test_valstruct_subsize_run \
@@ -2133,6 +2134,11 @@ $(BIN)/test_structlit_arrfield_run: test/wcc/949_structlit_arrfield_run.c \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_defdim_struct_run: test/wcc/951_defdim_struct_run.c \
+		$(BIN)/ww $(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_arraytoslice_run: test/wcc/953_arraytoslice_run.c \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
 		$(LIB)/libwwrt.a | $(BIN)