wcc: drop @test fns from non-T builds, both stages (harec check.c:3941)

Splice @test N_FNDECLs out of the unit after the body-check passes,
mirroring harec's checked-but-not-emitted: a broken @test body still
errors loudly in non-T; @test-free units are emission-unchanged.
910/997 table rows pin keep/test x non-T/-T, head+consecutive unlink,
undef-body reject, and plain-calls-dropped loud link-fail. w6c+wwdump
combined.ww regen. (#6-team)

test/wcc/data/attest_calldropped.ww

@@ -0,0 +1,18 @@
+// #6 fixture: a plain fn (the entry) CALLS a @test fn. In non-T the
+// @test def is spliced out but the CALL survives — harec-faithful: the
+// reference is left DANGLING and fails LOUDLY at link, never a silent
+// mis-link (ref/harec/src/check.c:3941 drops the decl; the call site's
+// symbol is never satisfied). Built non-T then linked: the link MUST
+// fail with an undefined reference to the dropped @test symbol (910
+// linkfail probe). No -T variant — a user main is -T-rejected (910).
+
+package data;
+
+@test fn calldropped_test() void = {
+	let a: i32 = 1;
+};
+
+export fn main() i32 = {
+	calldropped_test();
+	return 0;
+};

test/wcc/data/attest_nondrop.ww

@@ -0,0 +1,28 @@
+// #6 fixture: non-(-T) @test drop, harec-fidelity (ref/harec/src/
+// check.c:3941 — FN_TEST && !is_test is checked but not emitted). A
+// normal fn must survive a non-test build; uncalled @test fns must NOT
+// reach codegen. Under -T the synth entry calls the @test fns, so their
+// TEXT defs reappear. No imports — compiles straight to asm in both
+// modes for a TEXT-label grep (910/997 nondrop rows).
+//
+// Layout exercises the splice loop's unlink edges: a @test fn FIRST
+// (prev==nil head-unlink), a surviving plain fn, then TWO consecutive
+// @test fns (unlink-after-unlink). All three @test defs vanish non-T.
+
+package data;
+
+@test fn nondrop_test_a() void = {
+	let a: i32 = 1;
+};
+
+fn nondrop_keep() i32 = {
+	return 1;
+};
+
+@test fn nondrop_test_b() void = {
+	let a: i32 = 1;
+};
+
+@test fn nondrop_test_c() void = {
+	let a: i32 = 1;
+};

test/wcc/data/attest_undefbody.ww

@@ -0,0 +1,17 @@
+// #6 fixture: a @test body is type-checked in a non-test build even
+// though the fn is then spliced out. harec checks the body
+// (ref/harec/src/check.c:3913) BEFORE the append_decl skip (:3941), so
+// the splice is check-THEN-drop, never drop-then-skip-check. Pins that
+// placement decision: an undefined symbol in the @test body must be
+// caught LOUDLY in non-T (a pre-pass splice would silence it). Compiled
+// WITHOUT -T (910/997 plain-reject row).
+
+package data;
+
+fn keep() i32 = {
+	return 1;
+};
+
+@test fn undefbody_test() void = {
+	undefined_symbol_xyz();
+};