wcc/cgen: GAP-A.ptr global-array base — LEAQ name(SB) not (BP) (#11, both stages)

A global fixed array's .ptr (= &A[0]) must take the SB base, but cstage
emitted frame-relative LEAQ off(BP) for BOTH let- and def-global arrays
-> *A.ptr read frame garbage (0 instead of the element). cstage-SILENT;
wwstage def-global was a loud link-error. The .ptr read arm now gates
off==0 && (let_islet || def_isarraydef) -> LEAQ name(SB), reusing the
def-array index base predicate (cgen.c:4367, the #94/#231/#48 class).
Locals (off != 0) stay BP-relative -- the 14 toolchain backing-ptr sites
unaffected.

wwstage let-global was already correct; this adds the missing def-global
arm (cgenexpr.ww), converging cstage/wwstage byte-identical across all
three flavors (local / let-global / def-global) and closing a latent
cstage-only let-global cs!=ww divergence.

Byte-id 990-997 8/8 (corpus has no global .ptr); w6c/w6c_ww binaries move
(cgen changed). test/wcc/818 table-driven, build+run+byte-id per flavor.

Makefile

@@ -244,6 +244,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_arr_tagged_elem \
 	  $(BIN)/test_arr_infer_len \
 	  $(BIN)/test_arr_cap_reject \
+	  $(BIN)/test_arr_ptr_global \
 	  $(BIN)/test_def_arr_infer_len \
 	  $(BIN)/test_def_arr_len \
 	  $(BIN)/test_slice_str_global_zero \
@@ -642,6 +643,12 @@ $(BIN)/test_arr_cap_reject: test/wcc/817_arr_cap_reject.c $(BIN)/ww \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_arr_ptr_global: test/wcc/818_arr_ptr_global.c $(BIN)/ww \
+		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_def_arr_infer_len: test/wcc/814_def_arr_infer_len.c $(BIN)/ww \
 		$(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \